Revision summary help for the 9-1 AQA GCSE Combined Science Trilogy 1st biology exam paper - learning objectives

AQA Grade 9-1 GCSE Combined Science Trilogy 8464 Biology Paper 1 1F 1H papers - AQA GCSE Combined Science biology paper 1 Topic 1 "Cell biology", Topic 2 "Organisation", Topic 3 "Infection and response", Topic 4 "Bioenergetics"

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  1. ALL my unofficial GCSE (Grade 9-1) revision help summaries are based on the NEW 2016 official AQA (Grade 9-1) GCSE BIOLOGY/combined science trilogy biology specifications.

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Syllabus-specification CONTENT INDEX of revision summary notes

Revision summaries for AQA 9-1 GCSE Combined Science: Trilogy Biology Paper 1

What's assessed in this paper? Topics 1-4 (THIS PAGE)

SUMMARY of Topic 1. Cell biology (AQA 9-1 GCSE Combined Science Trilogy Biology Paper 1)

Topic 1.1 Cell structure * 1.2 Cell division * 1.3 Transport in cells

SUMMARY of Topic 2. Organisation  (AQA 9-1 GCSE Combined Science Trilogy Biology Paper 1)

Topic 2.1 Principles of organisation - Organisational hierarchy

Topic 2.2 Animal tissues, organs and organ systems * 2.3 Plant tissues, organs and systems

SUMMARY of Topic 3. Infection and response   (AQA 9-1 GCSE Combined Science Trilogy Biology Paper 1)

Topic 3.1 Communicable diseases

SUMMARY of Topic 4. Bioenergetics   (AQA 9-1 GCSE Combined Science Trilogy Biology Paper 1)

Topic 4.1 Photosynthesis * 4.2 Respiration


Revision summaries for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2

What's assessed in this paper? Topics 5-7 (on a separate page)

SUMMARY of Topic 5. Homeostasis and response  (AQA GCSE Combined Science Trilogy Biology Paper 2)

SUMMARY of Topic 6. Inheritance, variation and evolution  (AQA GCSE Comb. Sci. Trilogy Biology Paper 2)

SUMMARY of Topic 7. Ecology  (AQA 9-1 GCSE Combined Science Trilogy Biology Paper 2)


SUBJECT CONTENT of the AQA science syllabus-specifications biology part of 8464


Fundamental biological concepts and principles needed for BOTH biology papers.

You should have a basic understanding of the following biological principles and be able to apply them in either paper:

Key ideas in biology:

life processes depend on molecules whose structure is related to their function

the fundamental units of living organisms are cells, which may be part of highly adapted structures including tissues, organs and organ systems, enabling living processes to be performed effectively

living organisms may form populations of single species, communities of many species and ecosystems, interacting with each other, with the environment and with humans in many different ways

living organisms are interdependent and show adaptations to their environment

life on Earth is dependent on photosynthesis in which green plants and algae trap light from the Sun to fix carbon dioxide and combine it with hydrogen from water to make organic compounds and oxygen

organic compounds are used as fuels in cellular respiration to allow the other chemical reactions necessary for life

the chemicals in ecosystems are continually cycling through the natural world

the characteristics of a living organism are influenced by its genome and its interaction with the environment

evolution occurs by a process of natural selection and accounts both for biodiversity and how organisms are all related to varying degrees.

The structure and functioning of cells and how they divide by mitosis and meiosis from sections Cell biology and Meiosis.

That variation occurs when gametes fuse at fertilisation from section Sexual and asexual reproduction.

The two essential reactions for life on Earth: photosynthesis and respiration from sections Photosynthetic reaction and Aerobic and anaerobic respiration.

Metabolism is the sum of all the reactions happening in a cell or organism, in which molecules are made or broken down from section Metabolism.

All molecules are recycled between the living world and the environment to sustain life from section How materials are cycled.

You should be able to recall and use this knowledge in questions that link different areas of the specification to develop coherent arguments and explanations.


TOPICS for AQA GCSE Combined Science Trilogy: Biology Paper 1


Topic 1 Cell biology   

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 1, Topic 1 "Cell biology")

Know that cells are the basic unit of all forms of life and you should know how structural differences between types of cells enables them to perform specific functions within the organism. These differences in cells are controlled by genes in the nucleus. For an organism to grow, cells must divide by mitosis producing two new identical cells.

Know that if cells are isolated at an early stage of growth before they have become too specialised, they can retain their ability to grow into a range of different types of cells. This phenomenon has led to the development of stem cell technology. This is a new branch of medicine that allows doctors to repair damaged organs by growing new tissue from stem cells.



Topic 1.1 Cell structure 

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 1, Topic 1 "Cell biology")

1.1.1 Eukaryotes and prokaryotes

Know that plant and animal cells (eukaryotic cells) have a cell membrane, cytoplasm and genetic material enclosed in a nucleus.

Know that bacterial cells (prokaryotic cells) are much smaller and simpler in comparison. They have cytoplasm and a cell membrane surrounded by a cell wall. The genetic material is not enclosed in a nucleus. It is a single DNA loop and there may be one or more small rings of DNA called plasmids.

Be able to use prefixes centi, milli, micro and nano and you must be able to demonstrate an understanding of the scale and size of cells and be able to make order of magnitude calculations including the use of standard form.  

 

1.1.2 Animal and plant cells

You should be able to explain how the main sub-cellular structures, including the nucleus, cell membranes, mitochondria, chloroplasts in plant cells and plasmids in bacterial cells are related to their functions.

Most animal cells have the following parts:

a nucleus, which controls the activities of the cell

cytoplasm, in which most of the chemical reactions take place

a cell membrane, which controls the passage of substances into and out of the cell

mitochondria, which is where aerobic respiration takes place

ribosomes, which are where protein synthesis occurs.

In addition to the parts found in animal cells (listed above), plant cells often have:

chloroplasts, which absorb light to make food by photosynthesis

a permanent vacuole filled with cell sap.

Plant cells have a more rigid cell wall.

You must know the similarities and differences between plant, animal and bacterial cells.

Plant and algal cells also have a cell wall made of cellulose, which strengthens the cell.

You should be able to use estimations and explain what they should be used to judge the relative size or area of sub-cellular structures.

You should have observed and drawn plant and animal cells seen under a microscope.

 Introduction to plant and animal cell structure and function

 

1.1.3 Cell specialisation

You should be able to, when provided with appropriate information, explain how the structure of different types of cell relate to their function in a tissue, an organ or organ system, or the whole organism. Know that cells may be specialised to carry out a particular function e.g.

sperm cells, nerve cells and muscle cells in animals

root hair cells, xylem and phloem cells in plants.

You need to be able to describe the structure and function of these six cell types.

 

1.1.4 Cell differentiation

Know that as an organism develops, cells differentiate to form different types of cells.

Most types of animal cell differentiate at an early stage and then lose the ability to differentiate

Whereas many types of plant cells retain the ability to differentiate throughout life.

In mature animals, cell division is mainly restricted to repair and replacement. As a cell differentiates it acquires different sub-cellular structures to enable it to carry out a certain function. It has become a specialised cell.

 

1.1.5 Microscopy

You should be able to:

understand how microscopy techniques have developed over time,

explain how electron microscopy has increased understanding of sub-cellular structures,

and appreciate the differences in magnification and resolution that have both increased with technological development in microscopy.

Know and understand that an electron microscope has much higher magnification and resolving power than a light microscope. This means that it can be used to study cells in much finer detail. This has enabled biologists to see and understand many more sub-cellular structures.

You should appreciate the differences in magnification and resolution between a light microscope and an electron microscope. Be able to explain how electron microscopy has increased understanding of subcellular structures.

Be able to use prefixes centi (10-2), milli (10-3), micro (10-6) and nano (10-9) (expressing answers in standard form) and carry out calculations involving magnification, real size and image size using the formula:

magnification = size of image / size of real object  

With light microscopes you can see individual cells and large subcellular structures like the nucleus. With electron microscopes, using a beam of electrons instead of a beam of light, you gain a much higher resolution seeing much smaller objects e.g. the structures of mitochondria, chloroplasts, ribosomes and plasmids.

 


Topic 1.2 Cell division  

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 1, Topic 1 "Cell biology")

1.2.1 Chromosomes

Know that the nucleus of a cell contains chromosomes made of coiled DNA molecules, they are the genetic information. Each chromosome carries a large number of genes. In body cells the chromosomes are normally found in pairs.

Be able to use models and analogies to develop explanations of how cells divide.

 

1.2.2 Mitosis and the cell cycle

Know that cells divide in a series of stages called the cell cycle and you need to be able to describe the stages of the cell cycle including mitosis.

One of these stages is mitosis where the DNA, which has already been copied, divides. During the cell cycle the genetic material is doubled and then divided into two identical cells.

(1) Before a cell can divide it needs to grow and increase the number of sub-cellular structures such as ribosomes and mitochondria.

(2) The DNA replicates to form two copies of each chromosome. In mitosis one set of chromosomes is pulled to each end of the cell and the nucleus divides.

(3) Finally the cytoplasm and cell membranes divide to form two identical cells.

You need to understand the three overall stages of the cell cycle but do not need to know the different phases of the mitosis stage.

Cell division by mitosis is important in the growth and development of multicellular organisms.

You should be able to recognise and describe situations in given contexts where mitosis is occurring.

 

1.2.3 Stem cells

Know that a stem cell is an undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation.

You should be able to describe the function of stem cells in embryos, in adult animals and in the meristems in plants.

Stem cells from human embryos can be cloned and made to differentiate into most different types of human cells.

Stem cells from adult bone marrow can form many types of cells including blood cells.

Know that meristem tissue in plants can differentiate into any type of plant cell, throughout the life of the plant.

Knowledge and understanding of stem cell techniques are not required.

Treatment with stem cells may be able to help conditions such as diabetes and paralysis.

In therapeutic cloning an embryo is produced with the same genes as the patient. Stem cells from the embryo are not rejected by the patientís body so they may be used for medical treatment.

The use of stem cells has potential risks such as transfer of viral infection, and some people have ethical or religious objections against research and application of stem cells.

Stem cells from meristems in plants can be used to produce clones (genetically identical cells) of plants quickly and economically.

Rare species can be cloned to protect from extinction.

Crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers.

Be able to evaluate the practical risks and benefits, as well as social and ethical issues, of the use of stem cells in medical research and treatments.


Topic 1.3 Transport in cells  

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 1, Topic 1 "Cell biology")

1.3.1 Diffusion

Know that substances may move into and out of cells across the cell membranes via diffusion.

Diffusion is the spreading of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration.

Be able to recognise, draw and interpret diagrams that model diffusion.

Organisms must exchange substances with their environment i.e. take in nutrients or remove waste products.

Some of the substances transported in and out of cells by diffusion are oxygen and carbon dioxide in gas exchange, and of the waste product urea from cells into the blood plasma for excretion in the kidney.

Appreciate that large molecules cannot pass through the membrane.

You  should be able to explain how different factors affect the rate of diffusion, factors which affect the rate of diffusion are:

the difference in concentrations (concentration gradient)

the temperature

the surface area of the membrane.

A single-celled organism has a relatively large surface area to volume ratio. This allows sufficient transport of molecules into and out of the cell to meet the needs of the organism.

You should be able to calculate and compare surface area to volume ratios.

You should be able to explain the need for exchange surfaces and a transport system in multicellular organisms in terms of surface area to volume ratio.

You should be able to explain how the small intestine and lungs in mammals, gills in fish, and the roots and leaves in plants, are adapted for exchanging materials.

In multicellular organisms the smaller surface area to volume ratio means surfaces and organ systems are specialised for exchanging materials. This is to allow sufficient molecules to be transported into and out of cells for the organismís needs. The effectiveness of an exchange surface is increased by:

having a large surface area

a membrane that is thin, to provide a short diffusion path

in animals, having an efficient blood supply

in animals, for gaseous exchange being ventilated.

Be able to calculate and compare surface area to volume ratios.

You should understand the use of isotonic drinks and high energy drinks in sport.

 

1.3.2 Osmosis

Know that water may move across cell membranes via osmosis. Osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.

Revise the investigation into the effect of a range of  concentrations of salt or sugar solutions on the mass of plant tissue.

Be able to recognise, draw and interpret diagrams that model osmosis.

You should be able to:

use simple compound measures of rate of water uptake

use percentiles

calculate percentage gain and loss of mass of plant tissue

You should be able to plot, draw and interpret appropriate graphs relevant to osmosis.

 

1.3.3 Active transport

You should understand that active transport moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient). This requires energy from respiration. Without active transport, sufficient food for the organism may not be absorbed from the gut.

You should be able to link the structure of a root hair cell to its function. Active transport allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil. Plants require ions for healthy growth.

It also allows sugar molecules to be absorbed from lower concentrations in the gut into the blood which has a higher sugar concentration. Sugar molecules are used for cell respiration.

You should be able to explain and describe how diffusion, osmosis and active transport are used to transport materials in and out of cells and the differences between these three processes.

In terms of exchanging substances at various interfaces you should know all about gas exchange in the lungs, the function of villi in the small intestine, leaf structure and gas exchange and gills of fish enable an efficient gas exchange.


Topic 2 Organisation 

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 1, Topic 2 "Organisation")

Know that the human digestive system which provides the body with nutrients and the respiratory system that provides it with oxygen and removes carbon dioxide. These gases are dissolved materials that need to be moved quickly around the body in the blood by the circulatory system.

Know that damage to any of these systems can be debilitating if not fatal. Although there has been huge progress in surgical techniques, especially with regard to coronary heart disease, many interventions would not be necessary if individuals reduced their risks through improved diet and lifestyle.

Know how a plantís transport system is dependent on environmental conditions to ensure that leaf cells are provided with the water and carbon dioxide that they need for photosynthesis.



Topic 2.1 Principles of organisation - Organisational hierarchy

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 1, Topic 2 "Organisation")

Cells are the basic building blocks of all living organisms.

A tissue is a group of cells with a similar structure and function.

Organs are aggregations of tissues performing specific functions.

Organs are organised into organ systems, which work together to form organisms.

You should be able to develop an understanding of size and scale in relation to cells, tissues, organs and systems.


Topic 2.2 Animal tissues, organs and organ systems

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 1, Topic 2 "Organisation")

2.2.1 The human digestive system

This section does assumes knowledge of the digestive system studied in Key Stage 3 science.

The digestive system is an example of an organ system in which several organs work together to digest and absorb food.

You should be able to relate the action of enzymes to metabolism.

You should be able to describe the nature of enzyme molecules and relate their activity to temperature and pH changes.

You should be able to carry out rate calculations for chemical reactions. (rates of reaction notes)

Appreciate that you can measure rates of reaction by different methods.

Know that enzymes catalyse specific reactions in living organisms due to the specific shape of their active site.

Enzymes:

are biological catalysts that speed up chemical reactions in living organisms

are large proteins

catalyse a specific reaction due to the shape of the active site

are denatured by high temperature and extremes of pH due to changes in the shape of the active site

have an optimum temperature

have an optimum pH.

You should be able to use the Ďlock and key theoryí as a simplified model of enzyme action.

You should be able to recall the sites of production and the action of the enzymes amylase, proteases and lipases.

You should be able to understand simple word equations but no chemical symbol equations are required.

Digestive enzymes convert food into small soluble molecules that can be absorbed into the bloodstream.

Carbohydrases break down carbohydrates to simple sugars.

Amylase is a carbohydrase which breaks down starch.

Proteases break down proteins to amino acids.

Lipases break down lipids (fats) to glycerol and fatty acids.

Know that the products of digestion are used to build new carbohydrates, lipids and proteins.

Some glucose is used in respiration.

You should have used qualitative reagents to identify biological molecules such as starch, sugars and proteins (know the chemical tests for them).

Bile is made in the liver and stored in the gall bladder. It is alkaline to neutralise hydrochloric acid from the stomach. It also emulsifies fat to form small droplets which increases the surface area. The alkaline conditions and large surface area increase the rate of fat breakdown by lipase.

Also revise (1) The use qualitative reagents to test for a range of foods e.g. carbohydrates, lipids and proteins - including Benedictís test for sugars; iodine test for starch; and Biuret reagent for protein.

and (2) the investigation into the effect of a factor on the rate of an enzyme-controlled reaction (it could be concentration, temperature or pH) - investigation of the effect of pH on the rate of reaction of amylase enzyme.

You should have investigated the effect of pH on the rate of reaction of amylase enzyme by using a continuous sampling technique to determine the time taken to completely digest a starch solution at a range of pH values. Iodine reagent is to be used to test for starch every 30 seconds. Temperature must be controlled by use of a water bath or electric heater.

 

2.2.2 The heart and blood vessels

You should know the structure and functioning of the human heart and lungs, including how lungs are adapted for gaseous exchange.

The heart is an organ that pumps blood around the body in a double circulatory system. The right ventricle pumps blood to the lungs where gas exchange takes place. The left ventricle pumps blood around the rest of the body.

Knowledge of the blood vessels associated with the heart is limited to the aorta, vena cava, pulmonary artery, pulmonary vein and coronary arteries.

Knowledge of the names of the heart valves is not required.

Knowledge of the lungs is restricted to the trachea, bronchi, alveoli and the capillary network surrounding the alveoli.

Know that the natural resting heart rate is controlled by a group of cells located in the right atrium that act as a pacemaker.

Artificial pacemakers are electrical devices used to correct irregularities in the heart rate.

The body contains three different types of blood vessel: arteries, veins and capillaries.

You should be able to explain how the structure of these vessels relates to their functions.

You need to be able to use simple compound measures such as rate and carry out rate calculations e.g. breathing rate and pulse rate.

 

2.2.3 Blood

Blood is a tissue consisting of plasma, in which the red blood cells, white blood cells and platelets are suspended and know the function of each component.

Plasma transports proteins and other chemical substances around the body.

Red blood cells contain haemoglobin which binds to oxygen to transport it from the lungs to the tissues.

White blood cells help to protect the body against infection.

Platelets are fragments of cells which initiate the clotting process at wound sites.

You should be able to recognise different types of blood cells in a photograph or diagram, and explain how they are adapted to their functions - you should have observed and drawing blood cells seen under a microscope.

You need to able to evaluate risks related to use of blood products.

 

2.2.4 Coronary heart disease: a non-communicable disease

You should be able to evaluate the advantages and disadvantages of treating cardiovascular diseases by drugs, mechanical devices or transplant.

In evaluating methods of treatment you should bear in mind the benefits and risks associated with the treatment.

Appreciate the need and use of an artificial heart, valve replacement, artificial blood e.g. in emergency.

In coronary heart disease (an example of cardiovascular disease) layers of fatty material build up inside the coronary arteries, narrowing them. This reduces the flow of blood through the coronary arteries, resulting in a lack of oxygen for the heart muscle. Inserted stents are used to keep the coronary arteries open. Statins are widely used to reduce blood cholesterol levels which slows down the rate of fatty material deposit.

In some people heart valves may become faulty, preventing the valve from opening fully, or the heart valve might develop a leak. You should understand the consequences of faulty valves. Faulty heart valves can be replaced using biological or mechanical valves.

In the case of heart failure a donor heart, or heart and lungs can be transplanted. Artificial hearts are occasionally used to keep patients alive whilst waiting for a heart transplant, or to allow the heart to rest as an aid to recovery.

 

2.2.5 Health issues

You should be able to describe the relationship between health and disease and the interactions between different types of disease.

Health is the state of physical and mental wellbeing.

Diseases, both communicable diseases and non-communicable, are major causes of ill health. Other factors including diet, stress and life situations may have a profound effect on both physical and mental health.

Different types of disease may interact e.g.

Defects in the immune system mean that an individual is more likely to suffer from infectious diseases.

Viruses living in cells can be the trigger for cancers.

Immune reactions initially caused by a pathogen can trigger allergies such as skin rashes and asthma.

Severe physical ill health can lead to depression and other mental illness.

Be able to translate disease information between graph and numerical forms, construct and interpret frequency tables and diagrams, bar charts and histograms, and use a scatter diagram to identify a correlation between two variables.

You also need to understand the principles of sampling as applied to scientific data, including epidemiological data.

 

2.2.6 The effect of lifestyle on some non-communicable diseases

You should recall that many noncommunicable diseases are caused by the interaction of a number of factors (to include cardiovascular disease, some lung and liver diseases and diseases influenced by nutrition, including Type 2 diabetes).

Be able to explain the effect of lifestyle factors including diet, alcohol and smoking on the incidence of non-communicable diseases at local, national and global levels. Risk factors are linked to an increased rate of a disease. They can be:

Aspects of a personís lifestyle.

Substances in the personís body or environment.

A causal mechanism has been proven for some risk factors, but not in others.

The effects of diet, smoking and exercise on cardiovascular disease.

Obesity as a risk factor for Type 2 diabetes.

The effect of alcohol on the liver and brain function.

The effect of smoking on lung disease and lung cancer.

The effects of smoking and alcohol on unborn babies.

Carcinogens, including ionising radiation, as risk factors in cancer.

Be able to explain the human and financial cost of these non-communicable diseases to an individual, a local community, a nation or globally.

Many diseases are caused by the interaction of a number of factors.

Be able to interpret data about risk factors for specified diseases.

You should be able to understand the principles of sampling as applied to scientific data in terms of risk factors.

You should be able to translate information between graphical and numerical forms; and extract and interpret information from charts, graphs and tables in terms of risk factors.

You should be able to use a scatter diagram to identify a correlation between two variables in terms of risk factors.

 

2.2.7 Cancer

You should be able to describe cancer as the result of changes in cells that lead to uncontrolled growth and division.

Benign tumours and malignant tumours result from uncontrolled cell division.

Benign tumours are growths of abnormal cells which are contained in one area, usually within a membrane. They do not invade other parts of the body.

Malignant tumour cells are cancers. They invade neighbouring tissues and spread to different parts of the body in the blood where they form secondary tumours.

Scientists have identified lifestyle risk factors for various types of cancer including smoking, obesity, common viruses and UV exposure.

There are also genetic risk factors for some cancers.


Topic 2.3 Plant tissues, organs and systems

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 1, Topic 2 "Organisation")

2.3.1 Plant tissues and organ

You should be able to explain how the structures of plant tissues are related to their functions.

Plant tissues include:

epidermal tissues, which cover the plant

palisade mesophyll, which carries out photosynthesis

spongy mesophyll, which has air spaces for diffusion of gases

xylem and phloem, which transport substances around the plant

meristem tissue found at the growing tips of shoots and roots which will differentiate into different plant cells.

The leaf is a plant organ. The structures of tissues in the leaf are related to their functions.

Your knowledge should be limited to epidermis, palisade and spongy mesophyll, xylem and phloem and guard cells surrounding stomata.

You should have done observation and drawing of a transverse section of leaf.

 

2.3.2 Plant organ system

You should be able to explain how the structure of root hair cells, xylem and phloem are adapted to their functions.

You should be able to explain the effect of changing temperature, humidity, air flow (air movement) and light intensity on the rate of transpiration.

The roots, stem and leaves form a plant organ system for transport of substances around the plant.

Root hair cells are adapted for the efficient uptake of water by osmosis and mineral ions by active transport.

Xylem tissue transports water and mineral ions from the roots to the stems and leaves. It is composed of hollow tubes strengthened by lignin adapted for the transport of water in the transpiration stream.

You should be able to describe the process of transpiration and translocation, including the structure and function of the stomata.

Factors which affect the rate of transpiration are: temperature, humidity, air flow and light intensity.

Know that the role of stomata and guard cells are to control gas exchange and water loss.

Phloem tissue transports dissolved sugars from the leaves to the rest of the plant for immediate use or storage. The movement of food through phloem tissue is called translocation. Phloem is composed of tubes of elongated cells. Cell sap can move from one phloem cell to the next through pores in the end walls.

You don't need to know the detailed structure of phloem tissue or the mechanism of transport.

You should have done the experiments to:

Measuring the rate of transpiration by the uptake of water.

Investigating the distribution of stomata and guard cells.

Process data from investigations involving stomata and transpiration rates to find arithmetic means, understand the principles of sampling and calculate surface areas and volumes.

You need to understand and use simple compound measures such as the rate of reaction. Be able to translate information between graph and numerical form, plot and draw appropriate graphs, selecting appropriate scales for axes and extract and interpret information from graphs, charts and tables.


Topic 3 Infection and response 

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 1, Topic 3 "Infection and response")

Know that pathogens are microorganisms such as viruses and bacteria that cause infectious diseases in animals and plants. They depend on their host to provide the conditions and nutrients that they need to grow and reproduce. They frequently produce toxins that damage tissues and make us feel ill.

This section will explore how we can avoid diseases by reducing contact with them, as well as how the body uses barriers against pathogens. Once inside the body our immune system is triggered which is usually strong enough to destroy the pathogen and prevent disease.

 When at risk from unusual or dangerous diseases our body's natural system can be enhanced by the use of vaccination. Since the 1940s a range of antibiotics have been developed which have proved successful against a number of lethal diseases caused by bacteria. Unfortunately many groups of bacteria have now become resistant to these antibiotics. The race is now on to develop a new set of antibiotics.



Topic 3.1 Communicable diseases

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 1, Topic 3 "Infection and response")

3.1.1 Communicable (infectious) diseases

You should be able to explain how diseases caused by viruses, bacteria, protists and fungi are spread in animals and plants.

Be able to explain how the spread of diseases can be reduced or prevented. The spread of diseases can be reduced or prevented by eg simple hygiene measures, destroying vectors, isolation of infected individuals and vaccination.

Pathogens are microorganisms that cause infectious disease. Pathogens may be viruses, bacteria, protists or fungi. They may infect plants or animals and can be spread by direct contact, by water or by air. Pathogens are microorganisms such as viruses and bacteria that cause infectious diseases in animals and plants. They depend on their host to provide the conditions and nutrients that they need to grow and reproduce. They frequently produce toxins that damage tissues and make us feel ill.

This section explores how we can avoid diseases by reducing contact with them, as well as how the body uses barriers against pathogens. Once inside the body our immune system is triggered which is usually strong enough to destroy the pathogen and prevent disease.

Bacteria and viruses may reproduce rapidly inside the body. Bacteria may produce poisons (toxins) that damage tissues and make us feel ill.

Viruses live and reproduce inside cells, causing cell damage.

 

3.1.2 Viral diseases

Know that measles is a viral disease showing symptoms of fever and a red skin rash. Measles is a serious illness that can be fatal if complications arise. For this reason most young children are vaccinated against measles. The measles virus is spread by inhalation of droplets from sneezes and coughs.

HIV initially causes a flu-like illness. Unless successfully controlled with antiretroviral drugs the virus enters the lymph nodes and attacks the bodyís immune cells. Late stage HIV, or AIDS, occurs when the bodyís immune system becomes so badly damaged it can no longer deal with other infections or cancers. HIV is spread by sexual contact or exchange of body fluids such as blood which occurs when drug users share needles.

Tobacco mosaic virus (TMV) is a widespread plant pathogen affecting many species of plants including tomatoes. It gives a distinctive Ďmosaicí pattern of discolouration on the leaves which affects the growth of the plant due to lack of photosynthesis.

 

3.1.3 Bacterial diseases

Know that salmonella food poisoning is spread by bacteria ingested in food, or on food prepared in unhygienic conditions. In the UK, poultry are vaccinated against Salmonella to control the spread. Fever, abdominal cramps, vomiting and diarrhoea are caused by the bacteria and the toxins they secrete.

Gonorrhoea is a sexually transmitted disease (STD) with symptoms of a thick yellow or green discharge from the vagina or penis and pain on urinating. It is caused by a bacterium and was easily treated with the antibiotic penicillin until many resistant strains appeared. Gonorrhoea is spread by sexual contact. The spread can be controlled by treatment with antibiotics or the use of a barrier method of contraception such as a condom.

 

3.1.4 Fungal diseases

Rose black spot is a fungal disease where purple or black spots develop on leaves, which often turn yellow and drop early. It affects the growth of the plant as photosynthesis is reduced. It is spread in the environment by water or wind. Rose black spot can be treated by using fungicides and/or removing and destroying the affected leaves.

 

3.1.5 Protist diseases

Know that the pathogens that cause malaria are protists.

The malarial protist has a life cycle that includes the mosquito.

Malaria causes recurrent episodes of fever and can be fatal.

The spread of malaria is controlled by preventing the vectors, mosquitos, from breeding and by using mosquito nets to avoid being bitten.

 

3.1.6 Human defence systems

You should be able to explain the nonspecific defence systems of the human body against pathogens. The human body defends itself against the entry of pathogens including:

The skin is a barrier and produces antimicrobial secretions.

The nose traps particles which may contain pathogens.

The trachea and bronchi secrete mucus which traps pathogens and cilia waft the mucus to the back of the throat where it is swallowed.

The stomach produces acid which kills the majority of pathogens which enter via the mouth.

You should be able to explain the role of the immune system in the defence against disease. If a pathogen enters the body the immune system tries to destroy the pathogen. White blood cells help to defend against pathogens by:

phagocytosis, antibody production and antitoxin production.

 

3.1.7 Vaccination

You should be able to explain how vaccination will prevent illness in an individual, and how the spread of pathogens can be reduced by immunising a large proportion of the population.

Know that vaccination involves introducing small quantities of dead or inactive forms of a pathogen into the body to stimulate the white blood cells to produce antibodies. If the same pathogen re-enters the body the white blood cells respond quickly to produce the correct antibodies, preventing infection.

You do not need to know details of vaccination schedules and side effects associated with specific vaccines.

If a large proportion of the population is immune to a pathogen, the spread of the pathogen is very much reduced.

Be able to discuss the global use of vaccination in the prevention of disease.

 

3.1.8 Antibiotics and painkillers

You should be able to explain the use of antibiotics and other medicines in treating disease.

Antibiotics, such as penicillin, are medicines that help to cure bacterial disease by killing infective bacteria inside the body. It is important that specific bacteria should be treated by specific antibiotics.

The use of antibiotics has greatly reduced deaths from infectious bacterial diseases.

However, the emergence of strains resistant to antibiotics is of great concern.

Antibiotics cannot kill viral pathogens.

Painkillers and other medicines are used to treat the symptoms of disease but do not kill pathogens.

It is difficult to develop drugs that kill viruses without also damaging the bodyís tissues.

 

3.1.9 Discovery and development of drugs

You should be able to describe the process of discovery and development of potential new medicines, including preclinical and clinical testing. Know that traditionally drugs were extracted from plants and microorganisms.

The heart drug digitalis originates from foxgloves.

The painkiller aspirin originates from willow.

Penicillin was discovered by Alexander Fleming from the Penicillium mould.

Most new drugs are synthesised by chemists in the pharmaceutical industry. However, the starting point may still be a chemical extracted from a plant. 

New medical drugs have to be tested and trialled before being used to check that they are safe and effective.

New drugs are extensively tested for toxicity, efficacy and dose.

Preclinical testing is done in a laboratory using cells, tissues and live animals.

Clinical trials use healthy volunteers and patients.

Very low doses of the drug are given at the start of the clinical trial.

If the drug is found to be safe, further clinical trials are carried out to find the optimum dose for the drug.

In double blind trials, some patients are given a placebo, which does not contain the drug.

Patients are allocated randomly to groups so that neither the doctors nor the patients know who has received a placebo and who has received the drug until the trial is complete.

You should understand that the results of testing and trials are published only after scrutiny by peer review. This helps to prevent false claims.


Topic 4 Bioenergetics 

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 1, Topic 4 "Bioenergetics")

Know that sunlight is the ultimate source of energy for all living systems. Here you will explore how plants harness the Sunís energy in photosynthesis in order to make food. This process liberates oxygen which has built up over millions of years in the Earthís atmosphere. Both animals and plants use this oxygen to oxidise food in a process called aerobic respiration which transfers the energy that the organism needs to perform its functions. Conversely, anaerobic respiration does not require oxygen to transfer energy. During vigorous exercise the human body is unable to supply the cells with sufficient oxygen and it switches to anaerobic respiration. This process will supply energy but also causes the build-up of lactic acid in muscles which causes fatigue.



Topic 4.1 Photosynthesis 

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 1, Topic 4 "Bioenergetics")

 Photosynthesis, importance explained, limiting factors affecting rate

4.1.1 Photosynthetic reaction

Know that photosynthesis is represented by the word and symbol equations:

carbon dioxide + water == light ==>  glucose + oxygen

6CO2 + 6H2O == light ==>C6H12O6 + 6O2

You should be able to describe photosynthesis as an endothermic reaction in which energy is transferred from the
environment to the chloroplasts by light

 

4.1.2 Rate of photosynthesis

Know how the rate of photosynthesis may be affected by temperature, level of carbon dioxide, light intensity and amount of chlorophyll.

Be able to explain the effects of temperature, light intensity and carbon dioxide concentration on the rate of photosynthesis and to interpret graphs of photosynthesis rate involving one limiting factor.

You should be able to:

measure and calculate rates of photosynthesis

extract and interpret graphs of photosynthesis rate involving one limiting factor

plot and draw appropriate graphs selecting appropriate scale for axes

and translate information between graphical and numeric form

(HT only) Know that these factors interact and any one of them may be the factor that limits photosynthesis.

(HT only) You should be able to explain graphs of photosynthesis rate involving two or three factors and decide which is the limiting factor.

(HT only) You should understand and use inverse proportion Ė the inverse square law and light intensity in the context of photosynthesis.

(HT only) Limiting factors are important in the economics of enhancing the conditions in greenhouses to gain the maximum rate of photosynthesis while still maintaining profit.

(HT only) Be able to use data to relate limiting factors to the cost effectiveness of adding heat, light or carbon dioxide to greenhouses.

You should have done the practical to investigate the effect of a factor on the rate of photosynthesis.

 

4.1.3 Uses of glucose from photosynthesis

The glucose produced in photosynthesis may be used:

for respiration

converted into insoluble starch for storage

used to produce fat or oil for storage

used to produce cellulose, which strengthens the cell wall

used to produce amino acids for protein synthesis

Know that plants, to make proteins, also use nitrate ions that are absorbed from the soil.

Know the chemical tests to identify starch, glucose and proteins using simple qualitative reagent tests.


Topic 4.2 Respiration

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 1, Topic 4 "Bioenergetics")

4.2.1 Aerobic and anaerobic respiration

You should be able to describe cellular respiration as an exothermic reaction which is continuously occurring in living cells. The energy transferred supplies all the energy needed for living processes. Respiration in cells can take place aerobically (using oxygen) or anaerobically (without oxygen), to transfer energy

You should be able to compare the processes of aerobic and anaerobic respiration with regard to the need for oxygen, the differing products and the relative amounts of energy transferred.

Respiration in cells can take place aerobically (using oxygen) or anaerobically (without oxygen), to transfer energy.

Reactions which transfer energy to the environment are exothermic reactions.

Organisms need energy for chemical reactions to build larger molecules, movement and keeping warm.

Know that aerobic respiration is represented by the equations:

glucose + oxygen ===> carbon dioxide + water

C6H12O6 + 6O2 ===> 6CO2 + 6H2O

Anaerobic respiration in muscles is represented by the equation: glucose ===> lactic acid

The energy transferred supplies all the energy needed for living processes.

As the oxidation of glucose is incomplete in anaerobic respiration much less energy is transferred than in aerobic respiration.

Anaerobic respiration in plant and yeast cells is represented by the equations:

glucose ===> ethanol + carbon dioxide

C6H12O6 ===> 2C2H5OH + 2CO2

Anaerobic respiration in yeast cells is called fermentation and has economic importance in the manufacture of bread and alcoholic drink.

 

4.2.2 Response to exercise

Know that during exercise the human body reacts to the increased demand for energy. The heart rate, breathing rate and breath volume increase during exercise to supply the muscles with more oxygenated blood. If insufficient oxygen is supplied anaerobic respiration takes place in muscles. The incomplete oxidation of glucose causes a build up of lactic acid and creates an oxygen debt. During long periods of vigorous activity muscles become fatigued and stop contracting efficiently.

(HT only) Know that blood flowing through the muscles transports the lactic acid to the liver where it is converted back into glucose. Oxygen debt is the amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells.

You should have done the investigations into the effect of exercise on the body.

 

4.2.3 Metabolism

You should be able to explain the importance of sugars, amino acids, fatty acids and glycerol in the synthesis and breakdown of
carbohydrates, proteins and lipids.

Metabolism is the sum of all the reactions in a cell or the body.

The energy transferred by respiration in cells is used by the organism for the continual enzyme controlled processes of metabolism that synthesise new molecules.

Metabolism includes:

conversion of glucose to starch, glycogen and cellulose

the formation of lipid molecules from a molecule of glycerol and three molecules of fatty acids

the use of glucose and nitrate ions to form amino acids which in turn are used to synthesise proteins

respiration to release energy to power the chemical processes of life

breakdown of excess proteins to form urea for excretion.

You need to know the details of all of the five aspects above, and they are all covered in more detail in the relevant specification section but are linked together here under the heading 'metabolism'.


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