Biology Unit 2


Plants Producing Food

Energy Flows

Enzyme Action


Inheritance + variation

HideShow resource information

Structure of Animal + Plants Cells

Animal Cells + Plant Cells have...

a nucleus- holds the genetic information + controls cell activity

cytoplasm- needed for chemical reactions

a cell membrane- controls substances leaving/entering the cell

ribosomes- where protein synthesis takes place

mitochondria- release energy during respiration

BUT plant cells also have...

a cell wall- strenghtens the cell

chloroplasts- make food in photosynthesis

a permanent vacuole- filled with cell sap in the cytoplasm

1 of 13

Substances Entering + Leaving Cells

There are 3 ways substances can get in + out of cells.

Diffusion- when particles of gas or liquid are spread out.

It is the net movement of particles from an area of high concentration to an area of a lower concentration. Net movement explains which direction particles have moved.

Osmosisthe movement of water from an area of high concentration to an area of low concentration across a semi-permeable membrane.

- an isotonic solution is the same concentration as the cytoplasm inside the cell, so when added the cell is not affected

- a hypotonic solution has a greater concentration than the cell and more water moves into the cell than out

- a hypertonic solution has a lower water concentration than the cell, causing more water to move out than in 

 Active Transport- against the concentration gradient

2 of 13


carbon dioxide + water (+light energy) ---> glucose + oxygen

the cells in the leaves of plants contain chloroplasts, which contain chlorophyll. during photosynthesis, light energy is absorbed by chlorophyll and this energy is used to convert carbon dioxide (in the air) and water into glucose. the chemical reaction also produces oxygen which is released into the air.

Plants are perfectly adapted for a number of reasons:

most leaves are broad, larger surface area for light to fall on

they have air spaces to allow carbon dioxide in and oxygen out

they have veins which bring water to the leaves of the plant 

3 of 13

Limiting Factors of Photosynthesis

Light Intensity- brighter the light = faster the rate of photosynthesis

Carbon Dioxide Levels- plants need Co2 to photosynthesise and produce glucose

Temperature- photosynthesis is controlled by enzymes which work best at 40 degrees and are denatured if the temperature becomes too high

Water Availability- right amount of water must be available

4 of 13

Use Of Glucose + Nutrients

plants use glucose for..

respirationbreakdown of glucose using oxygen to provide energy for their cells

transport + storage- food must be transported to keep a constant supply of the food made

2 types of transport systems in a plant

phloem- made of living tissue. transports sugars made by photosynthesis around the plant (in all directions)

xylem- carries water + mineral irons from the soil around the plant (only upwards). made from what used to be living tissue

Nitrate Deficiency- wil not grow very big. 

Magnesium Deficiency- yellow leaves, Mg needed to make chlorophyll

5 of 13


In photosynthesis, green plants use some light energy from the sun and some is stored in the substances that make up the cells of the plant. This new plant material adds to the biomass (the living material in an animal or plant). All biomass originates from the sun. 

Pyramid of Biomass- PYRAMID! 

Pyramid of Numbers- size of section represents the number of organisms that there are in a particular food chain

Biomass is lost as the food chain goes up

6 of 13

Losing Energy

although the biomass an animal eats is a source of energy, not all the energy can be used. 

Energy is lost in...

Excretion- faeces, urine.

Respiration- in the cells

Movement- muscles contract

Warmth- keeping constant body temperature

Sankey Diagram can be used to show the loss of energy

7 of 13


Detritus Feeders- animals that feed on dead animals. worms

Decay Organisms- fungi, bacteria 

process of decay- detritus feeders eat dead animals/plants producing waste- decay organisms break down the waste and the dead plants and animals

decay is faster when the conditions are warm and wet. all of the produced materials from the waste are recycled

8 of 13

Carbon Cycle

Things that affect the levels of carbon dioxide going in and out of the atmosphere...

Photosynthesis- removes CO2

Respiration- releases CO2

Decay- releases CO2

Burning- releases CO2

9 of 13

Structure of Enzymes

an enzyme is a biological catalyst (speed up reactions). an enzyme is a protein and each one has its own shape. an enzyme has room for other molecules to fit in- active site. the shape of an active site changes with high temperatures and this means that the enzyme can no longer function (becomes denatured)

10 of 13

Limiting Factors of Enzyme Action

general reactions are quicker in warmer conditions where the molecules vibrate more violently + enzymes are able to further speed up reactions (up to a certain point). temperatures above 40 degrees tend to denature enzymes. 

a subject that is too acidic or too alkaline will also change the shape of the active site.

11 of 13

Aerobic Respiration

glucose + oxygen ---> carbon dioxide + water (+energy)

the site where respiration takes place is in the mitochondria. energy is produced in the process. this energy released is used for..

building up larger molecules from smaller ones

enabling muscle contraction in animals

maintaining a constant body temperature in mammals/birds

building nitrates, sugars and other nutrients in plants which are turned into amino acids and later into proteins

12 of 13


digestion requires breaking down large insoluble molecules to smaller soluble molecules. enzyme action assists this. there are a number of carbohydrases (enzymes) which are involved in the digestive system.

Amylase- produced in the salivary glands, pancreas, small intestine. catalyses the digestion of starch into sugars in the mouth and small intestine.

Lipase- produced in the pancreas, small intestine. catalyses the breakdown of lipids (fats) into fatty acids and glycerol. amylase and lipase work best with alkaline conditions so the liver produces bile which is stored in the gall bladder. bile is squirted into the small intestine which neutralises stomach acid, making the conditions slightly alkaline.

Protease- produced in the stomach, pancreas, small intestine. catalyses the breakdown of proteins into amino acids in the stomach and small intestine. protease enzymes in the stomach work best under acidic conditions. glands in the stomach produce hydrochloric acid to make it very acidic. this speeds up digestion.

13 of 13


Floss Cripps


osmosis is actually the movement of water from low to high, not high to low

Similar Biology resources:

See all Biology resources »