GCSE Biology Unit 2

Animal and Plant cells

Most cells have some structures in common. They have:

A nucleus to control the cell’s activities

Cytoplasm where many chemical reactions take place

A cell membrane that controls the movement of materials in and out of the cell

Mitochondria where energy is released during aerobic respiration

Ribosome’s are present where protein synthesis takes place

Plant and algal cells also have:

A rigid cell wall made of cellulose for support

Chloroplasts that contain chlorophyll for photosynthesis; the chloroplasts absorb light energy to make food

A permanent vacuole containing cell sap

Bacteria and Yeast

Bacterial cells have a cell membrane and a cell wall which is surrounded by cytoplasm

They do not have a nucleus so the genetic material is in the cytoplasm

When bacteria multiply they form a colony

Bacteria have the 3 c’s!!

Yeast is a single-celled organism

Yeast cells have a nucleus, cytoplasm and a membrane surrounded by a cell wall

Specialised cells

If a cell has many mitochondria, it must need a lot of energy e.g. muscle cell, sperm cell

If a cell has many ribosomes, it is making a lot of protein e.g. gland cells which produce enzymes

Diffusion

Diffusion is the spreading out of the particles of a gas, or of any substance in solution

The net movement into or out of cells depends on the concentration of the particles on each side of the cell membrane

Because the particles move randomly, there will be a net (overall) movement from an area of high concentration to an area of lower concentration

The difference in concentration between two areas is called the concentration gradient

The larger the difference in concentration, the faster the rate of diffusion

Examples are:

The diffusion of oxygen into the cells of the body from the bloodstream as the cells are respiring

The diffusion of carbon dioxide into actively photosynthesising plant cells

The diffusion of simple sugars and amino acids form the gut through the membranes

Photosynthesis

Carbon dioxide + water + (light and energy) = glucose + oxygen

Oxygen is released as a by-product of photosynthesis

Limiting Factors

Lack of light

Cold

Too little carbon dioxide

Temperature

How plants use glucose

Glucose produced from photosynthesis may be:

Converted into insoluble starch for storage

Used for respiration

Converted into fats or oils

Used to produce cellulose which strengths cell wall

Used to produce proteins

Plant and algae cells also need a supply of mineral ions such as nitrate ions in order to produce protein. Both absorb minerals from their surrounding environment

2 Converted and 3 used!!!

Organisms in their environment

Things that affect the distribution of organisms

Temperature

Availability of nutrients

Amount of light

Availability of water

Availability of oxygen

Availability of carbon dioxide

Enzymes

Proteins are made up of amino acids

The long chains are folded to produce specific shapes

The shape of a protein depends on its function

Proteins can be:

Muscles

Hormones Most Hormones Are Camp!

Antibodies

Catalysts

Chemical reactions in the body are controlled by enzymes

Enzymes are biological catalysts

The shape of an enzyme has an area where other molecules can fit (active site)

Enzymes can:

Build large molecules from many smaller ones

Change one molecule into another

Break down larger molecules into smaller ones

Reactions take place faster when it is warmer

The warmer the temperature, the faster the molecules move around and the more they collide with each other and with more energy

If the temperature gets too hot, the active site changes shape

The enzyme becomes denatured

Each enzyme works best at a particular pH

If the pH is too acidic or alkaline for