Revision summary help for the 9-1 AQA GCSE Combined Science Trilogy 2nd biology exam paper - learning objectives

AQA Grade 9-1 GCSE Combined Science Trilogy 8464 biology Paper 2 2F 2H papers - AQA GCSE Combined Science biology paper 2 Topic 5 "Homeostasis and response", Topic 6 "Inheritance, variation and evolution", Topic 7 "Ecology"

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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.

  2. Make sure you know whether you are doing separate science AQA GCSE grade 9-1 BIOLOGY OR AQA GCSE grade 9-1 Combined Science Trilogy biology.

  3. Also, make sure you know whether you are entered for a higher tier (HT) or a foundation tier (FT) AQA GCSE science-biology course, so watch out for the (HT only) 'markers'.

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  6. AQA GCSE grade 9-1 combined science trilogy biology 2 PAST PAPERS and specimen practice paper questions

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Syllabus-specification CONTENT INDEX of revision summary notes

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

What's assessed in this paper? Topics 1-4 (on a separate page)

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

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

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

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


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

What's assessed in this paper? Topics 5-7 (THIS PAGE)

SUMMARY Topic 5. Homeostasis and response (AQA 9-1 GCSE Combined Science Trilogy Biology Paper 2)

Topic 5.1 Homeostasis * 5.2 The human nervous system

Topic 5.3 Hormonal coordination in humans

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

Topic 6.1 Reproduction * 6.2 Variation and evolution

Topic 6.3 The development of understanding of genetics and evolution

Topic 6.4 Classification of living organisms

SUMMARY Topic 7. Ecology   (also Topic 7 AQA Combined Science Trilogy Paper 2)

Topic 7.1 Adaptations, interdependence and competition * 7.2 Organisation of an ecosystem

Topic 7.3 Biodiversity and the effect of human interaction on ecosystems


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


Fundamental biological concepts and principles needed for BOTH biology papers.


TOPICS for  AQA GCSE Combined Science: Trilogy Biology paper 2


Topic 5 Homeostasis and response 

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 5 "Homeostasis")

Know that cells in the body can only survive within narrow physical and chemical limits. They require a constant temperature and pH as well as a constant supply of dissolved food and water. In order to do this the body requires control systems that constantly monitor and adjust the composition of the blood and tissues.

These control systems include receptors which sense changes and effectors that bring about changes.

This section explores the structure and function of the nervous system and how it can bring about fast responses.

Know that its the hormonal system which usually brings about much slower changes. Hormonal coordination is particularly important in reproduction since it controls the menstrual cycle. An understanding of the role of hormones in reproduction has allowed scientists to develop not only contraceptive drugs but also drugs which can increase fertility.

Know that homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes.



Topic 5.1 Homeostasis

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 5 "Homeostasis")

Notes: Introduction to homeostasis and its function (negative feedback systems explained)

The Importance of homeostasis

You should be able to explain that homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes. You should be able to explain the importance of homeostasis in maintaining optimal conditions for enzyme action and all cell functions.

Homeostasis maintains optimal conditions for enzyme action and all cell functions.

In the human body, these include control of:

(i) blood glucose concentration, (ii) body temperature and (iii) water levels.

These automatic control systems may involve nervous responses or chemical responses.

All control systems include:

cells called receptors, which detect stimuli (changes in the environment)

coordination centres (such as the brain, spinal cord and pancreas) that receive and process information from receptors

effectors, muscles or glands, which bring about responses which restore optimum levels.


Topic 5.2 The human nervous system

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 5 "Homeostasis")

5.2.1 Structure and function

 

You should be able to explain how the structure of the nervous system is adapted to its functions.

The nervous system enables humans to react to their surroundings and to coordinate their behaviour.

Information from receptors passes along cells (neurones) as electrical impulses to the central nervous system (CNS). The CNS is the brain and spinal cord. The CNS coordinates the response of effectors which may be muscles contracting or glands secreting hormones.

stimulus ==> receptor ==> coordinator ==> effector ==> response

You should be able to explain how the various structures in a reflex arc relate to their function and understand why reflex actions are important. Reflex actions are automatic and rapid; they do not involve the conscious part of the brain. In a simple reflex action such as a pain withdrawal reflex:

impulses from a receptor pass along a sensory neurone to the CNS

at a junction (synapse) between a sensory neurone and a relay neurone in the CNS, a chemical is released that causes an impulse to be sent along a relay neurone

a chemical is then released at the synapse between a relay neurone and motor neurone in the CNS, causing impulses to be sent along a motor neurone to the effector

the effector is usually a muscle, in this case to withdraw the limb from the source of pain.

You should understand why reflex actions are important.

You should be able to extract and interpret data from graphs, charts and tables, about the functioning of the nervous system.

You should be able to translate information about reaction times between numerical and graphical forms.

Revise required practical 5: Investigating the effect of a factor on human reaction time. 


Topic 5.3 Hormonal coordination in humans

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 5 "Homeostasis")

5.3.1 Human endocrine system

You should be able to describe the principles of hormonal coordination and control by the human endocrine system.

The endocrine system is composed of glands which secrete chemicals called hormones directly into the bloodstream. The blood carries the hormone to a target organ where it produces an effect. Be able to compared to the nervous system the effects are slower but act for longer.

The pituitary gland in the brain is a ‘master gland’ which secretes several hormones into the blood in response to body conditions. These hormones in turn act on other glands to stimulate other hormones to be released to bring about effects.

You should be able to identify the position of the following on a diagram of the human body:

pituitary gland, pancreas, thyroid, adrenal gland, ovary and testes.

 

5.3.2 Control of blood glucose concentration

Know that blood glucose concentration is monitored and controlled by the pancreas.

If the blood glucose concentration is too high, the pancreas produces the hormone insulin that causes glucose to move from the blood into the cells. In liver and muscle cells excess glucose is converted to glycogen for storage.

You should be able to explain how insulin controls blood glucose (sugar) levels in the body.

Type 1 diabetes is a disorder in which the pancreas fails to produce sufficient insulin. It is characterised by uncontrolled high blood glucose levels and is normally treated with insulin injections.

In Type 2 diabetes the body cells no longer respond to insulin produced by the pancreas. A carbohydrate controlled diet and an exercise regime are common treatments. Obesity is a risk factor for Type 2 diabetes.

You should be able to compare Type 1 and Type 2 diabetes and explain how they can be treated.

You should be able to extract information and interpret data from graphs that show the effect of insulin in blood glucose levels in both people with diabetes and people without diabetes.

(HT only) If the blood glucose concentration is too low, the pancreas produces glucagon that causes glycogen to be converted into glucose and released into the blood.

(HT only) You  should be able to explain how glucagon interacts with insulin in a negative feedback cycle to control blood glucose (sugar) levels in the body.

 

5.3.3 Hormones in human reproduction 

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 5 "Homeostasis")

 You should be able to describe the roles of hormones in human reproduction, including the menstrual cycle.

During puberty reproductive hormones cause secondary sex characteristics to develop.

Oestrogen is the main female reproductive hormone produced in the ovary. At puberty eggs begin to mature and one is released approximately every 28 days. This is called ovulation.

Testosterone is the main male reproductive hormone produced by the testes and it stimulates sperm production.

Several hormones are involved in the menstrual cycle of a woman.

Follicle stimulating hormone (FSH) causes maturation of an egg in the ovary.

Luteinising hormone (LH) stimulates the release of the egg.

Oestrogen and progesterone are involved in maintaining the uterus lining.

(HT only) You should be able to explain the interactions of FSH, oestrogen, LH and progesterone, in the control of the menstrual cycle.

(HT only) You should be able to extract and interpret data from graphs showing hormone levels during the menstrual cycle.

 

5.3.4 Contraception 

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 5 "Homeostasis")

You should be able to evaluate the different hormonal and non-hormonal methods of contraception.

Fertility can be controlled by a variety of hormonal and nonhormonal methods of contraception. These include:

oral contraceptives that contain hormones to inhibit FSH production so that no eggs mature

injection, implant or skin patch of slow release progesterone to inhibit the maturation and release of eggs for a number of months or years

barrier methods such as condoms and diaphragms which prevent the sperm reaching an egg

intrauterine devices which prevent the implantation of an embryo or release a hormone

spermicidal agents which kill or disable sperm

abstaining from intercourse when an egg may be in the oviduct

surgical methods of male and female sterilisation.

Be able to show why issues around contraception cannot be answered by science alone.

Be able to explain everyday and technological applications of science; evaluate associated personal, social, economic and environmental implications; and make decisions based on the evaluation of evidence and arguments.

 

5.3.5 The use of hormones to treat infertility (HT only) 

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 5 "Homeostasis")

 You should be able to explain the use of hormones in modern reproductive technologies to treat infertility.

This includes giving FSH and LH in a 'fertility drug' to a woman whose own level of FSH is too low to stimulate eggs to mature. She may then become pregnant in the normal way.

In Vitro Fertilisation (IVF) treatment.

IVF involves giving a mother FSH and LH to stimulate the maturation of several eggs.

The eggs are collected from the mother and fertilised by sperm from the father in the laboratory.

The fertilised eggs develop into embryos.

At the stage when they are tiny balls of cells, one or two embryos are inserted into the mother's uterus (womb).

Note that developments of microscopy techniques have enabled IVF treatments to develop.

You should understand social and ethical issues associated with IVF treatments.

Although fertility treatment gives a woman the chance to have a baby of her own:

it is very emotionally and physically stressful

the success rates are not high

it can lead to multiple births which are a risk to both the babies and the mother.

Be able to evaluate from the perspective of patients and doctors the methods of treating infertility.

 

5.3.6 Negative feedback (HT only) 

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 5 "Homeostasis")

You should be able to explain the roles of thyroxine and adrenaline in the body as negative feedback systems.

Adrenaline is produced by the adrenal glands in times of fear or stress. It increases the heart rate and boosts the delivery of oxygen and glucose to the brain and muscles, preparing the body for ‘flight or fight’.

Thyroxine from the thyroid gland stimulates the basal metabolic rate. It plays an important role in growth and development.

Thyroxine levels are controlled by negative feedback.

Be able to interpret and explain simple diagrams of negative feedback control.


Topic 6 Inheritance, variation and evolution 

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 6 "Inheritance, variation and selection")

In Topic 6 you will discover how the number of chromosomes are halved during meiosis and then combined with new genes from the sexual partner to produce unique offspring. Gene mutations occur continuously and on rare occasions can affect the functioning of the animal or plant. These mutations may be damaging and lead to a number of genetic disorders or death. Very rarely a new mutation can be beneficial and consequently, lead to increased fitness in the individual. Variation generated by mutations and sexual reproduction is the basis for natural selection; this is how species evolve.

An understanding of these processes has allowed scientists to intervene through selective breeding to produce livestock with favoured characteristics. Once new varieties of plants or animals have been produced it is possible to clone individuals to produce larger numbers of identical individuals all carrying the favourable characteristic.

Scientists have now discovered how to take genes from one species and introduce them in to the genome of another by a process called genetic engineering. In spite of the huge potential benefits that this technology can offer, genetic modification still remains highly controversial.



Topic 6.1 Reproduction  

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 6 "Inheritance, variation and selection")

6.1.1 Sexual and asexual reproduction

You should understand that meiosis leads to non-identical cells being formed while mitosis leads to identical cells being formed. Sexual reproduction involves the joining (fusion) of male and female gametes:

sperm and egg cells in animals

pollen and egg cells in flowering plants.

In sexual reproduction there is mixing of genetic information which leads to variety in the offspring. The formation of gametes involves meiosis.

Asexual reproduction involves only one parent and no fusion of gametes. There is no mixing of genetic information. This leads to genetically identical offspring (clones). Only mitosis is involved.

 

6.1.2 Meiosis

You should be able to explain how meiosis halves the number of chromosomes in gametes and fertilisation restores the full number of chromosomes.

Cells in reproductive organs divide by meiosis to form gametes.

When a cell divides to form gametes:

copies of the genetic information are made

the cell divides twice to form four gametes, each with a single set of chromosomes

all gametes are genetically different from each other.

Gametes join at fertilisation to restore the normal number of chromosomes. The new cell divides by mitosis. The number of cells increases. As the embryo develops cells differentiate.

Knowledge of the stages of meiosis is not required but you should have seen modelling of the behaviour of chromosomes during meiosis.

 

6.1.3 DNA and the genome  

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 6 "Inheritance, variation and selection")

You should be able to describe the structure of DNA and define genome.

The genetic material in the nucleus of a cell is composed of a chemical called DNA. DNA is a polymer made up of two strands forming a double helix. The DNA is contained in structures called chromosomes.

A gene is a small section of DNA on a chromosome. Each gene codes for a particular sequence of amino acids, to make a specific protein.

The genome of an organism is the entire genetic material of that organism. The whole human genome has now been studied and this will have great importance for medicine in the future.

You should be able to discuss the importance of understanding the human genome. This is limited to the:

search for genes linked to different types of disease

understanding and treatment of inherited disorders

use in tracing human migration patterns from the past.

 

6.1.4 Genetic inheritance  

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 6 "Inheritance, variation and selection")

You should be able to explain the following ten terms:

gamete, chromosome, gene, allele, dominant, recessive, homozygous, heterozygous, genotype and phenotype.

Some characteristics are controlled by a single gene, such as: fur colour in mice; and red-green colour blindness in humans. Each gene may have different forms called alleles.

The alleles present, or genotype, operate at a molecular level to develop characteristics that can be expressed as a phenotype.

A dominant allele is always expressed, even if only one copy is present. A recessive allele is only expressed if two copies are present (therefore no dominant allele present).

If the two alleles present are the same the organism is homozygous for that trait, but if the alleles are different they are heterozygous.

Most characteristics are a result of multiple genes interacting, rather than a single gene.

You should be able to understand the concept of probability in predicting the results of a single gene cross, but recall that most phenotype features are the result of multiple genes rather than single gene inheritance.

You should be able to use direct proportion and simple ratios to express the outcome of a genetic cross.

You should be able to complete a Punnett square diagram and extract and interpret information from genetic crosses and family trees.

(HT only) You should be able to construct a genetic cross by Punnett square diagram and use it to make predictions using the theory of probability.

 

6.1.5 Inherited disorders

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 6 "Inheritance, variation and selection")

Know that some disorders are inherited. These disorders are caused by the inheritance of certain alleles.

Polydactyly (having extra fingers or toes) is caused by a dominant allele.

Cystic fibrosis (a disorder of cell membranes) is caused by a recessive allele.

You should make informed judgements about the economic, social and ethical issues concerning embryo screening, given appropriate information.

You should appreciate that embryo screening and gene therapy may alleviate suffering but consider the ethical issues which arise.

 

6.16 Sex determination

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 6 "Inheritance, variation and selection")

Know that ordinary human body cells contain 23 pairs of chromosomes.

22 pairs control characteristics only, but one of the pairs carries the genes that determine sex.

In females the sex chromosomes are the same (XX).

In males the chromosomes are different (XY).

You should to be able to carry out a genetic cross to show sex inheritance.

You should understand and be able to use direct proportion and simple ratios in genetic crosses


Topic 6.2 Variation and evolution  

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 6 "Inheritance, variation and selection")

6.2.1 Variation

You should be able to describe simply how the genome and its interaction with the environment influence the development of the phenotype of an organism.

Differences in the characteristics of individuals in a population is called variation and may be due to differences in:

the genes they have inherited (genetic causes)

the conditions in which they have developed (environmental causes)

a combination of genes and the environment.

You should be able to:

state that there is usually extensive genetic variation within a population of a species

recall that all variants arise from mutations and that:

most have no effect on the phenotype

some influence phenotype

very few determine phenotype.

Know that mutations occur continuously. Very rarely a mutation will lead to a new phenotype. If the new phenotype is suited to an environmental change it can lead to a relatively rapid change in the species (can eventually result in a new species - speciation)

6.2.2 Evolution

You should be able to describe evolution as a change in the inherited characteristics of a population over time through a process of natural selection which may result in the formation of a new species.

The theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed more than three billion years ago.

You should be able to explain how evolution occurs through natural selection of variants that give rise to phenotypes best suited to their environment.

If two populations of one species become so different in phenotype that they can no longer interbreed to produce fertile offspring they have formed two new species.

Be able to use the theory of evolution by natural selection in an explanation

 

6.2.3 Selective breeding

You should be able to explain the impact of selective breeding of food plants and domesticated animals.

Selective breeding (artificial selection) is the process by which humans breed plants and animals for particular genetic characteristics. Humans have been doing this for thousands of years since they first bred food crops from wild plants and domesticated animals.

Selective breeding involves choosing parents with the desired characteristic from a mixed population. They are bred together. From the offspring those with the desired characteristic are bred together. This continues over many generations until all the offspring show the desired characteristic.

The characteristic can be chosen for usefulness or appearance:

Disease resistance in food crops.

Animals which produce more meat or milk.

Domestic dogs with a gentle nature.

Large or unusual flowers.

Appreciate that selective breeding can lead to ‘inbreeding’ where some breeds are particularly prone to disease or inherited defects.

Be able to explain the benefits and risks of selective breeding given appropriate information and consider related ethical issues.

 

6.2.4 Genetic engineering

You should be able to describe genetic engineering as a process which involves modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic.

Plant crops have been genetically engineered to be resistant to diseases or to produce bigger better fruits.

Bacterial cells have been genetically engineered to produce useful substances such as human insulin to treat diabetes.

You should be able to explain the potential benefits and risks of genetic engineering in agriculture and in medicine and that some people have objections.

In genetic engineering, genes from the chromosomes of humans and other organisms can be ‘cut out’ and transferred to cells of other organisms.

Crops that have had their genes modified in this way are called genetically modified (GM) crops. GM crops include ones that are resistant to insect attack or to herbicides. GM crops generally show increased yields.

Concerns about GM crops include the effect on populations of wild flowers and insects. Some people feel the effects of eating GM crops on human health have not been fully explored.

Modern medical research is exploring the possibility of genetic modification to overcome some inherited disorders.

(HT only) You should be able to describe the main steps in the process of genetic engineering.

(HT only) In genetic engineering:

enzymes are used to isolate the required gene; this gene is inserted into a vector, usually a bacterial plasmid or a virus

the vector is used to insert the gene into the required cells

genes are transferred to the cells of animals, plants or microorganisms at an early stage in their development so that they develop with desired characteristics.

(HT only) Be able to interpret information about genetic engineering techniques and to make informed judgements about issues concerning cloning and genetic engineering, including GM crops.


Topic 6.3 The development of understanding of genetics and evolution

6.3.1 Evidence for evolution

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 6 "Inheritance, variation and selection")

You should be able to describe the evidence for evolution including fossils and antibiotic resistance in bacteria.

The theory of evolution by natural selection is now widely accepted.

Evidence for Darwin’s theory is now available as it has been shown that characteristics are passed on to offspring in genes. There is further evidence in the fossil record and the knowledge of how resistance to antibiotics evolves in bacteria.

Appreciate that data is now available to support the theory of evolution.

 

6.3.2 Fossils

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 6 "Inheritance, variation and selection")

 Fossils are the ‘remains’ of organisms from hundreds of thousands of years ago, which are found in rocks. Fossils may be formed:

from parts of organisms that have not decayed because one or more of the conditions needed for decay are absent

when parts of the organism are replaced by other materials as they decay

as preserved traces of organisms, such as footprints, burrows and rootlet traces.

Many early forms of life were soft-bodied, which means that they have left few traces behind. What traces there were have been mainly destroyed by geological activity. This is why scientists cannot be certain about how life began on Earth.

We can learn from fossils how much or how little different organisms have changed as life developed on Earth.

Be able to extract and interpret information from charts, graphs and tables such as evolutionary trees.

You should appreciate why the fossil record is incomplete and understand how scientific methods and theories about evolution have developed over time.
 

6.3.3 Extinction

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 6 "Inheritance, variation and selection")

Extinctions occur when there are no remaining individuals of a species still alive.

You should be able to describe factors which may contribute to the extinction of a species.

eg extinction may be caused by: changes to the environment over geological time, new predators, new diseases, new, more successful, competitors, a single catastrophic event such as a massive volcanic eruptions or collisions with asteroids.

 

6.3.4 Resistant bacteria

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 6 "Inheritance, variation and selection")

Know that bacteria can evolve rapidly because they reproduce at a fast rate.

Mutations of bacterial pathogens produce new strains. Some strains might be resistant to antibiotics, and so are not killed. They survive and reproduce, so the population of the resistant strain rises. The resistant strain will then spread because people are not immune to it and there is no effective treatment.

MRSA is resistant to antibiotics. To reduce the rate of development of antibiotic resistant strains:

doctors should not prescribe antibiotics inappropriately, such as treating non-serious or viral infections

patients should complete their course of antibiotics so all bacteria are killed and none survive to mutate and form resistant strains.

 the agricultural use of antibiotics should be restricted

The development of new antibiotics is costly and slow and is unlikely to keep up with the emergence of new resistant strains.


Topic 6.4 Classification of living organisms

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 6 "Inheritance, variation and selection")

Know that traditionally living things have been classified into groups depending on their structure and characteristics in a system described by Carl Linnaeus.

Linnaeus classified living things into kingdom, phylum, class, order, family, genus and species. Organisms are named by the binomial system of genus and species.

You should be able to use information given to show understanding of the Linnaean system.

You should be able to describe the impact of developments in biology on classification systems.

As evidence of internal structures became more developed due to improvements in microscopes, and the understanding of biochemical processes progressed, new models of classification were proposed.

Due to evidence available from chemical analysis there is now a ‘three-domain system’ developed by Carl Woese. In this system organisms are divided into:

Archaea (primitive bacteria usually living in extreme environments)

Bacteria (true bacteria)

Eukaryota (which includes protists, fungi, plants and animals).

Evolutionary trees are a method used by scientists to show how they believe organisms are related. They use current classification data for living organisms and fossil data for extinct organisms. Be able to interpret evolutionary trees.


Topic 7 Ecology 

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 7 "Ecology")

Know that the Sun is a source of energy that passes through ecosystems. Materials including carbon and water are continually recycled by the living world, being released through respiration of animals, plants and decomposing microorganisms and taken up by plants in photosynthesis.

All species live in ecosystems composed of complex communities of animals and plants dependent on each other and that are adapted to particular conditions, both abiotic and biotic. These ecosystems provide essential services that support human life and continued development.

In order to continue to benefit from these services humans need to engage with the environment in a sustainable way.

Appreciate how humans are threatening biodiversity as well as the natural systems that support it and be able to consider some actions we need to take to ensure our future health, prosperity and well-being.



Topic 7.1 Adaptations, interdependence and competition

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 7 "Ecology")

7.1.1 Communities

You should be able to describe:

different levels of organisation in an ecosystem from individual organisms to the whole ecosystem

the importance of interdependence and competition in a community.

You should be able to, when provided with appropriate information:

suggest the factors for which organisms are competing in a given habitat

suggest how organisms are adapted to the conditions in which they live.

An ecosystem is the interaction of a community of living organisms (biotic) with the non-living (abiotic) parts of their environment.

To survive and reproduce, organisms require a supply of materials from their surroundings and from the other living organisms there.

Plants in a community or habitat often compete with each other for light and space, and for water and mineral ions from the soil.

Animals often compete with each other for food, mates and territory.

Within a community each species depends on other species for food, shelter, pollination, seed dispersal etc. If one species is removed it can affect the whole community. This is called interdependence. A stable community is one where all the species and environmental factors are in balance so that population sizes remain fairly constant.

You should be able to extract and interpret information from charts, graphs and tables relating to the interaction of organisms within a community.

 

7.1.2 Abiotic factors

You should be able to explain how a change in an abiotic factor would affect a given community given appropriate data or context.

Abiotic (non-living) factors which can affect a community are:

light intensity,

temperature,

moisture levels,

soil pH and mineral content,

wind intensity and direction,

carbon dioxide levels for plants,

oxygen levels for aquatic animals.

You should be able to extract and interpret information from charts, graphs and tables relating to the effect of abiotic factors on organisms within a community.

 

7.1.3 Biotic factors

You should be able to explain how a change in a biotic factor might affect a given community given appropriate data or context.

Biotic (living) factors which can affect a community are:

availability of food,

new predators arriving,

new pathogens,

one species outcompeting another so the numbers are no longer sufficient to breed

e.g. such as the introduction of grey squirrels into southern Britain outcompeted the native red squirrels.

You should be able to extract and interpret information from charts, graphs and tables relating to the effect of biotic factors on organisms within a community.

 

7.1.4 Adaptations

You should be able to explain how organisms are adapted to live in their natural environment, given appropriate information.

Organisms have features (adaptations) that enable them to survive in the conditions in which they normally live. These adaptations may be structural, behavioural or functional.

Some organisms live in environments that are very extreme, such as at high temperature, great pressure, or high salt concentration. These organisms are called extremophiles. Bacteria living in deep sea vents are extremophiles.

Some notes on Adaptations, lots of examples explained including extremophiles


Topic 7.2 Organisation of an ecosystem  

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 7 "Ecology")

7.2.1 Levels of organisation

You should understand that photosynthetic organisms are the producers of biomass for life on Earth.

Feeding relationships within a community can be represented by food chains. All food chains begin with a producer which synthesises molecules. This is usually a green plant which makes glucose by photosynthesis.

A range of experimental methods using transects and quadrats are used by ecologists to determine the distribution and abundance of species in an ecosystem.

In relation to abundance of organisms you should be able to:

understand the terms mean, mode and median

calculate arithmetic means

plot and draw appropriate graphs selecting appropriate scales for the axes.

Producers are eaten by primary consumers, which in turn may be eaten by secondary consumers and then tertiary consumers.

Consumers that eat other animals are predators, and those eaten are prey. In a stable community the numbers of predators and prey rise and fall in cycles. You should be able to interpret graphs used to model these cycles.

Required practical activity 9: You should have measured the population size of a common species in a habitat and use sampling techniques to investigate the effect of a factor on the distribution of this species.

 

7.2.2 How materials are cycled

You should:

recall that many different materials cycle through the abiotic and biotic components of an ecosystem

be able to explain the importance of the carbon and water cycles to living organisms.

All materials in the living world are recycled to provide the building blocks for future organisms.

The carbon cycle returns carbon from organisms to the atmosphere as carbon dioxide to be used by plants in photosynthesis.

The water cycle provides fresh water for plants and animals on land before draining into the seas. Water is continuously evaporated and precipitated.

You are not expected to study the nitrogen cycle.

You should be able to explain the role of microorganisms in cycling materials through an ecosystem by returning carbon to the atmosphere as carbon dioxide and mineral ions to the soil.

Be able to interpret and explain the processes in diagrams of the carbon cycle, the water cycle.


Topic 7.3 Biodiversity and the effect of human interaction on ecosystems 

7.3.1 Biodiversity   

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Biology Paper 2, Topic 7 "Ecology")

Biodiversity is the variety of all the different species of organisms on earth, or within an ecosystem.

A great biodiversity ensures the stability of ecosystems due to the interdependencies of one species on another for food, shelter and the maintenance of the physical environment. 

Biodiversity helps the stability of ecosystems by reducing the dependence of one species on another for food, shelter and the maintenance of the physical environment.

The future of the human species on Earth relies on us maintaining a good level of biodiversity.

Many human activities are reducing biodiversity and only recently have measures been taken to try to stop this reduction.

Be able to explain how waste, deforestation and global warming have an impact on biodiversity.

 

7.3.2 Waste management

 Rapid growth in the human population and an increase in the standard of living mean that increasingly more resources are used and more waste is produced. Unless waste and chemical materials are properly handled, more pollution will be caused.

Pollution can occur:

in water, from sewage, fertiliser or toxic chemicals

in air, from smoke and acidic gases such as sulfur dioxide and nitrogen dioxide, which contributes to acid rain

on land, from landfill and from fertilisers and toxic chemicals such as pesticides and herbicides, which may be washed from land into water.

Pollution kills plants and animals which can reduce biodiversity.

 

7.3.3 Land use

Appreciate that humans reduce the amount of land available for other animals and plants by building, quarrying, farming and dumping waste.

The destruction of peat bogs, and other areas of peat to produce garden compost, reduces the area of this habitat and thus the variety of different plant, animal and microorganism species that live there (decreasing biodiversity).

The decay or burning of the peat releases carbon dioxide into the atmosphere.

You need to understand the conflict between the need for cheap available compost to increase food production and the need to conserve peat bogs and peatlands as habitats for biodiversity and to reduce carbon dioxide emissions.

 

7.3.4 Deforestation

Large-scale deforestation in tropical areas has occurred to:

provide land for cattle and rice fields to provide more food

grow crops from which biofuels, based on ethanol, can be produced.

Be able to evaluate the environmental implications of deforestation eg

This destruction of large areas of trees has:

increased the release of carbon dioxide into the atmosphere (because of burning and the activities of microorganisms)

reduced the rate at which carbon dioxide is removed from the atmosphere by photosynthesis and ‘locked up’ in wood for hundreds of years

led to reduction in biodiversity of both plant species and the animals that live there.

 

7.3.5 Global warming

You should be able to describe some of the biological consequences of global warming.

Levels of carbon dioxide and methane in the atmosphere are increasing, and contribute to ‘global warming’.

You need to understand that the scientific consensus about global warming and climate change is based on systematic reviews of thousands of peer reviewed publications.

Be able to explain why evidence is uncertain or incomplete in a complex context.

 

7.3.6 Maintaining biodiversity
You should be able to describe both positive and negative human interactions in an ecosystem and explain their impact on biodiversity.

Scientists and concerned citizens have put in place programmes to reduce the negative effects of humans on ecosystems and biodiversity.

These include:

breeding programmes for endangered species

protection and regeneration of rare habitats

reintroduction of field margins and hedgerows in agricultural areas where farmers grow only one type of crop

reduction of deforestation and carbon dioxide emissions by some governments

recycling resources rather than dumping waste in landfill.

Be able to evaluate given information about methods that can be used to tackle problems caused by human impacts on the environment.

Be able to explain and evaluate the conflicting pressures on maintaining biodiversity given appropriate information.


PAST PAPERS   (Practice exam question papers for revising AQA 9-1 GCSE Combined Science Trilogy Biology Paper 2, Topic 5 "Homeostasis and response", Topic 6 "Inheritance, variation and evolution", Topic 7 "Ecology")



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