Edexcel Biology – 1) The Nature and Variety of Living Organisms

A. Characteristics of Living Organisms

1) Require nutrition – plants make their own food; animals eat other organisms.

2) Respire – release energy from their food.

3) Excrete – get rid of waste product.

4) Respond to stimuli – sensitive to changes in their surroundings.

5) Move – action of muscles in animals; slow grow movement in plants.

6) Control their internal conditions – maintain a steady state inside the body.

7) Reproduce – produce offspring.

8) Grow and develop – increase in size and complexity, using material from their food.

B. Variety of Living Organisms

Eukaryotic vs Prokaryotic

Eukaryotic – having a nucleus. Their cells contain a nucleus surrounded by a cell membrane, along
with other membrane bounded organelles (specialised subunit within a cell) such as mitochondria
and chloroplasts.

Prokaryotic – before nucleus. These are organisms made of simpler cells, has no nucleus,
mitochondria or chloroplasts.

Eukaryotic Prokaryotic

Plants Bacteria

Animals Viruses

Fungi

Protoctists
Eukaryotic - Plants

- Multicellular organisms.
- Contain chloroplasts, able to carry out photosynthesis.
- Cellulose cell walls.
- Store carbohydrates as starch or sucrose.
- Examples: flowering plants – maize / corns; herbaceous legume – beans / peas.

Eukaryotic -Animals

- Multicellular organisms.
- Do not contain chloroplasts, unable to carry out photosynthesis.
- No cell walls.
- Usually have nerve coordination, able to move from one place to another.
- Store carbohydrates as glycogen.
- Examples: mammals – human; insects – fly / mosquitoes.

Eukaryotic -Fungi

- Can be multicellular (mushrooms / moulds) or unicellular (yeasts).

- Unable to carry out photosynthesis.
- Body organised into mycelium made from thread-like structures called hyphae, which contain
many nuclei.
- Chitin made cell walls. (ie not cellulose)
- Saprotrophic nutrition: extracellular secretion of digestive enzymes onto food material and
absorption of the organic products.
- May store carbohydrates as glycogen.
- Examples: multicellular - mucor; unicellular – yeasts.
Eukaryotic -Protoctists

- Microscopic (very tiny) unicellular organisms.

- Some has features like an animal cell, eg. Amoeba, that lives in pond water.
- Some are like plants and has chloroplasts, eg Algae.
- Some are pathogens that cause disease, eg Plasmodium that cause malaria.

Prokaryotic – Bacteria

- Microscopic (very tiny) unicellular organisms.

- Have a cell wall, cell membrane, cytoplasm and plasmids.
- Some have flagella and can swim.
- No nucleus but contain a circular chromosome of DNA.
- Most feed off other living or dead organisms, some contains chlorophyll and able to carry out
photosynthesis.
- Some are used to make food, eg Lactobacillus Bulgaricus, a rod-shaped bacterium used in the
production of yoghurt from milk.
- Others are pathogens that cause disease, eg Pneumococcus, a spherical bacterium that acts
as the pathogen causing pneumonia.
Prokaryotic – Viruses

- Parasites, parasitise both animals and plants.

- Only reproduce inside living cells called host.
- Not made of cells.
- No nucleus or cytoplasm, only a core DNA / RNA surrounded by a protein coat.
- No Characteristics of living organisms except reproduction.
Edexcel Biology – 2) Structure and Functions in Living Organisms
A. Level of Organisation – Organelles, Cells, Tissues, Organs and Systems
Organelles – specialised subunit within a cell. Part of a cells, as organs are to human.

Cells – All living organisms are composed of units called cells.

Tissues – Cells with similar functions are group together to form tissues.

Organ – A collection of several tissue carrying out a particular function is called organ.

Systems – Several different organs working together for jobs is a system.

B. Cell Structure

Animals and Plants Plants Only

Cytoplasm Cell Wall

Nucleus Vacuole

Ribosomes Chloroplast

Cell Membrane

Mitochondria
Structures in both animals and plants:

Cytoplasm – living material that makes up a cell.

Nucleus – Largest organelles. Controls activities of the cell. Contains Chromosomes (ie Genes or DNA).
Genes control which protein the cell can make. Instructions are carried out of the nucleus to the
cytoplasm.

Ribosomes – tiny structures in the cytoplasm where the protein are assembled.

Cell membrane – a thin layer surrounds the cell. Forms a boundary between the cytoplasm of the cell
and the outside. Partially permeable – some chemicals can into the cell and some can pass out.
Selectively permeable – it can control the movement of some substances.

Mitochondria – carry out respiration, release energy for the cell to use.

Structures in plants only:

Cell wall – layer of non-living material called cellulose outside the cell membrane of plant cells.
Cellulose is tough and keeps shape, resists the pressure from water inside the plants. Cell wall is
porous – has many holes and freely permeable.

Vacuole – large centre space surrounded by a membrane, filled with cell sap – stores watery liquid of
dissolved sugar and minerals.

Chloroplast – cells of green parts of plants such as leaves. Absorbs light energy to make food through
photosynthesis. Contains chlorophyll - green pigment.

C. Biological Molecules
Carbohydrates 𝐶6 𝐻12 𝑂6

- Carbohydrates: means carbon and water.

- Glucose: cells oxide it to release energy. Sweet and soluble.
- Fructose: fruit sugar. Sweet and soluble.
- Lactose: milk sugar. Sweet and soluble.
- Sucrose: table sugar. The main sugar that is transported through plant stems. Sweet and soluble.
- Starch: Only found in plant tissues. Large and insoluble. As storage carbohydrates in plant such
as potatoes, rice and wheat.
- Glycogen: Similar to starch but found in animals.
- Cellulose: cell wall is a type of carbohydrates but humans are not able to digest. Instead, it is
used as dietary fibre.
- Monosaccharides: means carbohydrates with single sugar molecule including glucose and
fructose.
- Disaccharides: means carbohydrates with 2 sugar molecules joined together including sucrose
and lactose.
 - Polysaccharides: means carbohydrates with many sugar molecules joined together. They are
large, long chain sugar molecules called polymer of sugar, including starch, glycogen and
cellulose.

Lipids (Fats and Oils)

- Lipids: same as carbohydrate they contain carbon, hydrogen and oxygen only, but the proportion
of oxygen in Lipids is much lower.
- Building blocks: Glycerol and Fatty Acid.
- Glycerol: oily liquid, also known as glycerine. Used frequently in cosmetics
- Fatty Acid: many different types, which gives different types of lipid in food.
- Lipid: a glycerol molecule is joined to 3 fatty acid molecules.
- Cholesterol: a kind of lipid compound.
Proteins

- Proteins: each protein is made up of 20 sub-unit called amino acids.

- Amino Acids: All amino acids contain 4 elements – carbon, hydrogen, oxygen and nitrogen. Two
of the amino acids contain sulphur as well.
- The amino acids are linked together to form long chains, usually folded up or twisted into spirals.
- Their shapes determine their functions.
- The order of amino acids determines their shapes.
- Many different combinations, hence many kinds of protein. Some carry out specific functions
such as enzymes and
Enzymes

- A kind of protein. Biological catalyst.

- Control chemical reaction in cells.
- Catalyst: a chemical which speeds up reaction without using up itself. It takes part in the
chemical reaction, but afterward is unchanged and free to catalyst more reactions.
- How activities in cell are controlled: the nucleus contains the genes, which control the
production of enzymes, which catalyse the reactions in the cytoplasm.
- Why do humans need enzymes? Body temperature is low (37 degree Celsius), without catalyst
most chemical reactions in cell happen too slowly to keep the life.

How enzymes work?

- Substrate: The molecule that the enzyme acts on.

- Active Site: each enzyme has a small area on its surface called active site.
- The substrate attaches to the active site, reaction takes place, final product is formed.
- It lowers the energy needed for reaction to start, allowing the product to be formed more easily.
- Enzymes also catalyse reactions where large molecules are built up from smaller molecules.
Several smaller molecules attach to the active site and the large molecule is formed.
- Lock and Key Model of enzyme reaction: Substrates will only fit into the active site of a particular
enzyme, like fitting key into a lock.
- After the enzyme has catalysed a reaction, the product is released from the active site. The
enzyme is free to act on more substrates.

-
Factors Affecting Enzymes – Temperature and pH

Temperature

- Optimum Temperature: 37 degrees Celsius for enzymes in human body.

- As enzyme is heated up to the optimum temperature, the rise in temperature increases the rate
of reaction.
- As temperature increases, the kinetic energy of the enzyme and the substrate increases, they
collide more often, means reaction will take place more frequently.

- However, above the optimum, the enzyme’s protein molecules are broken down by heat.
- Denaturing: above 40 degrees Celsius, the enzyme is destroyed.
- Denaturing changes the shape of the active site; substrate will no longer fit into it.
- Denaturing is permanent, the enzyme will no longer catalyse the reaction.
- Not all enzyme have an optimum temperature of 37 degrees Celsius.

pH

- pH inside cells is neutral with pH 7.

- Optimum pH: most Enzymes work best at pH 7
- Either side of the optimum, the pH affects the structure of the enzyme molecule and changes
the shape of the active site, so that the substrate will not fit into it well.
Practical: Starch, Glucose, Protein and Lipid
Practical: Effect of Temperature on Enzyme Activity