Introduction to plant & animal CELL STRUCTURE & FUNCTION

Doc Brown's Biology Revision Notes

Suitable for GCSE/IGCSE/O level Biology/Science courses or equivalent

 


(a) CELLS

 All living things are made up of cells, the building blocks of life.

 A cell is the smallest unit of life able to control its own activities, BUT, it relies on the rest of the organism (if multicellular) or the surroundings (if unicellular) to provide it with raw materials i.e. nutrients and removal of waste material.

 You should know and understand  that the structures of different types of cells are related to their functions.

 You should know and understand the similarities and differences between animal cells, bacteria and plant cells.

Cells can be either eukaryotic or prokaryotic in character.

Eukaryotes are organisms made of eukaryotic cells, which are complex cells, and all plants and animals are made up of such cells. They are usually multi-cellular organisms, but can consist of one cell e.g. yeast.

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

Prokaryotes, are smaller, simpler and single celled organisms (unicellular) eg bacteria are prokaryotic cells.

The different parts of a cell are referred to as subcellular structures.

A diagrammatic comparison of animal cells, plant cells and bacteria cells

- their similarities and differences in sub-cellular structures.

 


(b) ANIMAL CELLS including humans! (eukaryotes)

Most animal cells have the following five parts in these eukaryotic cells - the so called subcellular structures, and, remember, plants cells usually have the same five components too.

1. Cell membrane

The cell contents i.e. the sub-cellular structures like cytoplasm, nucleus, (small vacuoles), mitochondria etc. are all held together by the soft cell membrane which controls the passage of substances in and out of the cell. Because not everything can pass through the membrane, it is described as a semi-permeable or a partially permeable membrane.

The cell membrane allows the free passage of water and gases but may act as a selective barrier to other chemicals. The cell membrane also contains receptor molecules that are used in cell communication e.g. by hormones.

2. Mitochondria

The energy releasing chemistry of respiration occurs in the mitochondria, which is where most energy is released in respiration - eg the aerobic 'burning' of glucose to release energy.

e.g. glucose + oxygen ==> carbon dioxide + water + energy

The equation of aerobic respiration, an exothermic chemical reaction and catalysed by the appropriate enzymes.

glucose  +  oxygen  ===>  carbon dioxide  +  water

C6H12O6(aq)  +  6O2(g)  ===>  6CO2(g)  +  6H2O(l)  +  energy

RESPIRATION - aerobic and anaerobic in plants, fungi and animals, conditions, substrates etc.  gcse biology revision notes

Mitochondria are the power house of the cells and contain all the enzymes needed for the chemical reactions that provide the chemical energy for any of the cells functions.

Liver cells carry out lots of metabolic reactions so lots of energy needed, so they contain a lot more mitochondria.

Similarly, muscle cells need lots of energy eg to contract, so again, they have a lot more mitochondria than other cells to supply the energy for the physical work animals perform.

3. Cytoplasm

Cytoplasm is a jelly like fluid (gel-like) in which most of the cells chemical reactions take place and most of these reactions are catalysed by enzymes (biological catalysts) which control the rate of these reactions. Anaerobic respiration take place in the cytoplasm, but aerobic respiration takes place in the mitochondria.

4. Nucleus

The cell nucleus contains all the genetic material, the DNA codes of the genes in the chromosomes which control the cells functions and the cell division in replication. The nucleus controls the activities of the cell by sending instructions to the cytoplasm. The genetic material is organised into chromosomes. chromosomal /DNA contains the instructions for making proteins eg that make up tissue or enzymes.

5. Ribosomes

Ribosomes are involved in the translation of the genetic material from the chromosomes, they can decode the DNA to carry out various chemical synthesis e.g. ribosomes are where protein synthesis from amino acids occurs in the cell - the protein 'factory'! They are too small to be seen by a light microscope.

Other features

Glycogen granules

Stored food for respiration.

Small vacuoles

Some animal cells may have several small vacuoles

Some differences between animal, plant and bacteria cells

Animal cells are much larger than bacterial cells, with important differences from plant cells.

Animal cells, unlike plant cells, do not have (i) a rigid cell wall, (ii) a permanent vacuole and (iii) chloroplasts.

 

Note: What is an organelle? An organelle is a specialized part of a cell having some specific function, a sort of cell organ. Organelles are only found in eukaryotes (plant and animal cells). The nucleus, mitochondria, ribosomes and chloroplasts are examples of organelles.


(c) PLANT and algal CELLS (eukaryotes)

Plant cells are much larger than bacterial cells, with important differences from animal cells.

Like animal cells, plants cells have (1) a cell membrane, (2) mitochondria, (3) cytoplasm, (4) nucleus and (5) ribosomes, all of which perform the same functions as described above in the animal cell section (b) above.

The three extra principal different sub-cellular structures that plant cells have plant and animal cells do not are: (i) a rigid cell wall, (ii) chloroplasts and (iii) a permanent vacuole - animal cells do NOT have these three features.

You need to be able to describe the function of the components of a plant cell including chloroplast, large vacuole, cell wall, cell membrane, mitochondria, cytoplasm and nucleus (see diagram and notes below) and know the differences between plant and animal cells.

 

(i) Plant and algal cells have a more rigid cell wall made of cellulose, which strengthens the cell, supports it and therefore the plant's structure as a whole.

 

(ii) Chloroplasts the sites of photosynthesis

Chloroplasts can absorb light energy to make food via chlorophyll in photosynthesis

The chloroplasts contain the green chlorophyll molecules which are involved in the energy absorbing process of photosynthesis. The chlorophyll molecules absorb the light energy from the sun to promote the endothermic reaction below. The chloroplasts must also contain all the enzymes to catalyse the whole series of complex reactions to make sugars - the equation below is a greatly simplified summary!

sunlight energy + carbon dioxide + water ==> sugars (e.g. glucose) + oxygen

6H2O(l) + 6CO2(g) ====> C6H12O6(aq) + 6O2(g)

Therefore chloroplasts are the site of food production for the plant. The sugars may be used directly as a source of energy or converted to starch grains - the plant's food store (and part of our food store as well!).

Chlorophyll absorbs mainly in the violet-blue and orange-red regions of the visible spectrum, hence it appears green, the light NOT absorbed.

 

(iii) Large permanent vacuole

Most plant cells have a single large permanent vacuole containing cell sap, a dilute solution of mineral salts and sugars. It maintains the internal pressure to support the cell. The central vacuole is a cellular organelle found in plant cells. It is often the largest organelle in the cell. The central vacuole is surrounded by a membrane and functions to hold useful materials and wastes. It also functions to maintain the proper pressure within the plant cells to provide structure and support for the growing plant.
 

Other features

Starch grains

Stored food for respiration from the glucose made by photosynthesis.

 


(d) BACTERIA (are prokaryotes)

Bacterial cells, single-celled microorganisms, are much smaller than plant or animal cells with some quite distinct and different sub-cellular features.

A prokaryotic bacterial cell consists of cytoplasm within a membrane surrounded by a cell wall.

Bacteria do not have a real nucleus, chloroplasts or mitochondria.

Cell wall and inner membrane

The cell contents i.e. the cytoplasm, DNA etc. are all held together within the cell wall by the surface membrane which controls the passage of substances in and out of the cell. The surrounding cell wall gives bacteria extra structural support.

Cytoplasm

The jelly like fluid in which most of the cells chemical reactions take place with the aid of enzyme catalysts. Although they do not have mitochondria, bacterial cells can still respire aerobically in the cytoplasm.

Chromosomal DNA - the genetic material is not confined in a nucleus which doesn't exist in bacteria

The genes are not in a distinct true nucleus, the genetic material is a sort of jumbled cluster comprising of one long circular strand of DNA floating free in the cytoplasm sometimes accompanied by one or more small rings of DNA called plasmids. As with any other cells the string of DNA controls the cell's activities and cell division for replication.

This single chromosome controls the cells functions and the cell division in replication.

The chromosomal DNA moves freely around in the cytoplasm and is not confined in a distinct nucleus as in plant and animal cells.

Plasmid DNA, not part of the chromosome

Plasmids are small hoops of extra DNA that are separate from the chromosomal DNA.

Plasmids contain genes that help tolerance against drugs and this drug resistance can be passed from one bacteria to another - a problem in dealing with bacterial infectious diseases.

This is how the bacteria MSRA have evolved and become so dangerous.

Not all prokaryote cells contain plasmids.

Shape and Flagella (flagella plural, flagellum singular)

Bacteria come in all sorts of shapes e.g. rods, spirals etc. and some have a tail!

The flagellum is a long thin tail, hair-like structure that projects out of the body of the cell, and can rotate to move the bacteria along.

Some bacterial cells have more than one flagella (flagellum).

Each flagellum is effectively driven by a tiny biochemical electric motor with moving parts, mostly made of proteins!

The flagellum enables a bacterium away from harmful substances (e.g. toxins) and move towards beneficial materials like nutrients or oxygen.

It is quite a remarkable piece of biochemical engineering - bioengineering!

Ribosomes

As with other cells, the place of protein synthesis from decoding genetic material from chromosome material.

Other comments on prokaryotes like bacteria

Unlike eukaryotic cells, prokaryotic cells do not contain a defined nucleus nor do they contain mitochondria or chloroplasts.


(e) YEAST CELLS (eukaryotes)

Yeast is used in the production of alcoholic beverages eg beer, wine etc. and in bread making.

A yeast cell, a single-cell microorganism, has a nucleus, cytoplasm, mitochondria enclosed in a cell membrane which is surrounded by a cell wall.

diagram?

 


(f) CELL SPECIALISM - an introduction is on another page


aqa gcse 9-1 biology: 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. Similarities and differences between 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. Be able to recognise, draw and interpret images of cells. 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.


 

 

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