B2 Revision

  • Created by: MasonT
  • Created on: 05-04-14 17:34


Diffusion - Is the spreading out of particles from an area of high concentration to an area of low concentrations

1 of 25

How plants use glucose

To get other useful substances.

Making cell walls 
Glucose is converted into cellulose for making strong cell walls.

Making proteins 
Makes amino acids, which are used to make proteins. 

Stored in seeds 
Turned into lipids to store in seeds

Stored a starch 
Stored for when photosynthesis isn't happening

2 of 25


Greenhouses can be used to make sure tthat crops get the right amount of carbon
dioxide, light and heat

Condtions can be altered by using parafin heaters, artificial light, and ventilation.
This makes sure that there is no limiting factor for photosynthesis, so a good crop is produced. 

3 of 25

Distribution of organisms

5 things affecting distribution

  • Temperture.
  • Avaliability of water.
  • Avaliability of oxygen and carbon dioxide. 
  • Avaliability of nutrients.
  • Amount of light.

Is a square frame, enclosing a known area

Is a line, which you count what organisms are touching the line. 
Or put quadrats next to the transect line.

Reliability and validty

Reliability - Repeatable and reproducible. Large sample size. Random samples.           

Validty - Control all variables, otherwise other factors that are not enviromental may be affecting the results.

4 of 25


Enzymes are catalysts produced by living things which increases the speed of a reaction without being changed or used in the reaction.

Chemical reactions usually involve being either split apart or joined together.

Enyzmes are proteins, made up of chains of amino acids.

Every enzyme has a unique shape for a certain substance.

Enymes have to be at the right

  • Temperture
  • PH

Otherwise, if not the bond holding the enzyme together breaks 

5 of 25

Enzymes and digestion

Digestive enzymes break down big moecules into smaller ones

Amylase converts starch into sugars

  • Salivary glands
  • Pancreas
  • Small intestines

Protease converts proteins into amino acids

  • Stomach
  • Pancreas
  • Small intestines

Lipase converts Lipids into Glycerol and fatty acids

  • Pancreas
  • Small intestines

Bile neutralises stomach acid and emulsifies fats

6 of 25

Enzymes and digestion

Salivary glands - Produces amylase enzymes in the saliva.

Liver - Produces bile which neutralises stomach acid and emulsifies fat.

Gall bladder - Where bile is stored, before released into small intestines.

Large intestine - Water is absorbed from food.

Rectum - Where faeces stored before going through anus.

Small intestine - Produces protease, amylase and lipase enzymes and absorbs food.

Pancreas - Produces protease, amylase and lipase enzymes.

Stomach - Pummels food with muscular wall and produces the protease enzyme.

7 of 25

Respiration/Aerobic respiration

Respiration is the process of releasing energy from glucose, which goes on in every cell.

Aerobic respiration is respiration using oxygen. It's the most efficient way to release energy from glucose. 

Most aerobic respiration happens inside mitochondria.

Glucose + Oxygen --> Carbon dioxide + Water + Energy

Respiration releases energy:

  • To build large molecules from smaller ones.
  • Allows muscles to contract.
  • In mammals the energy is used to keep body temperture steady.
  • Plants build up amino acids, which are built up into proteins
8 of 25


Exercise increases the heart rate

As more glucose and oxygen are needed to supply the muscle cells.

Also, extra carbon dioxide needs to be removed from the mucle cells, so blood has to flow faster.

  • Breathing rate increases, to meet the extra oxygen demand.
  • Heart rate increases.

Some glucose is stored as glycogen in exercise.

This is because glucose is used fast in exercise, so some of the glycogen is converted back to glucose to provide more energy.

9 of 25

Respiration/Anaerobic respiration

Anaerobic respiration is used if there is not enough energy.

When the body can't supply enough oxygen to the muscles, they start doing anaerobic respiration.

Glucose --> Energy + Lactic acid

Lactic acid causes muscle fatigue and becomes painful.

Anaerobic respiration produces a lot less energy than aerobic respiration.


After anaerobic respiration, oxygen needs to be repaid to the muscles.

Oxygen debt is breathing in the amount of oxygen to get rid of the lactic acid.

10 of 25

Uses of enzymes

Enzymes are used in:

  • Biological detergent 
  • Changing food
  • Industries

For biological deterents, enzymes are ideal as they can remove stains, food and blood.

Digesting enzymes can be used for baby food so it's easier for them to eat.

Enzymes pros and cons

  • Specific, so only catalyse reactions that are wanted.
  • Lower temperture means a lower cost as saves energy
  • Enzymes work a long time
  • They are biodegradeable
  • Some people can develop allergies
  • Enzymes can be denatured, by a change in temperture or PH
  • Enzymes can be expensive to produce.
  • Contamination of enzymes with other substancescan affect the reaction
11 of 25

Uses of enzymes continued

Carbohydrases enzyme turns starch syrup into sugar syrup.

Isomerase enzyme turns glucose syrup into frucose syrup.

12 of 25


DNA = Deoxyribose nucleic acid.

Chromosomes are long molecules of DNA to put an organism together and make it work.

  • Contains all the instructions.
  • Found in nucleus.

A gene is a section of DNA.

  • A gene codes for a specific protein.
  • Contains all the instructions to make a specific proetein.
  • Only 20 amino acids are used, but make thousands of proteins.
  • Genes simply tell cells what order to put the amino acids together.
  • This determines what type of cell they are.

DNA Fingerprinting

  • Forensic science
  • Paternity testing
13 of 25

Mitosis - Cell division

Mitosis is when a cell reproduces itself by splitting to form two identical offspring.

Mitosis makes new cells for growth and repair.

  • In a body cell, the DNA is all spread out.
  • When the DNA gets a signal to divide, it duplicates its DNA. Forming X-Shaped chromosomes.
  • The chromosomes then line up at the centre, then fibres pull them apart.
  • Cell membrane then forms around each sets of chromosomes.
  • These become the nuclei of the 2 new cells.
  • Lastly, the cytoplasm divides. Leaving 2 identical new cells.

Asexual reproduction also used mitosis.

Some organims reproduce by mitosis

14 of 25

Meiosis - Cell division

Meiosis produces cells which have half the number of chromosomes.

  • The cell duplicates its DNA
  • In the first division the cells line up
  • The pairs of chromosomes are then pulled apart, so each new cell ony has 1 copy of each chromosome.
  • In the second division, the chromosomes line up in the centre. Then the cell is divided again.
  • Leaving 4 gametes each with only a single set of  chromosomes.



 Before the cells start to divide , the DNA is duplicated. The cell then divides twice, during which the choromosomes line up in pairs and are pulled apaart. Four gametes are produced, each with a single set of chromosomes.

15 of 25

Stem cells

Stem cells - undifferentiated cells that can develop into different types of/specialised cells.

Embryonic stem cells can turn into any type of cell.

Differentiation - Process by which a cell changes to become specialised for its job.


Stem cells are found in early human embryos.

Adults do have stem cells, but only found in certain places, and aren't as versatile as emryonic stem cells.

16 of 25

Stem cells Continued

Embryonic stem cells can be used to replace faulty cells in sick people and make nerve cells for paralysed people (paralysis).

Blood diseases can be treated with bone marrow transplants.

Stem cells can treat disorders as they can be grown in particular types of cells, which then can be used to replace faulty cells.

Stem cell research arquments.

  • Some people feel the embryos shouldn't be used tor experiments.
  • Since each one is a potential human life.
  • Some people feel scientists should find other ways to get stem cells, without using embryos.
  • Some people feel we should focus more on people that already exist than the embryos.
  • Fertily clinics often dispose embryos, so could be used in research.
  • Any research done has to follow strict guidelines.
17 of 25

X and Y chromosomes

Chromosomes control whether you're male or female.

There are 22 matched pairs of chromosomes in every human body cell.

The 23rd pair is labelled ** or XY

This determines whether your male or female.

Men: XY, Female: **

Genetic diagrams show the possible combinations of gametes

18 of 25

George Mendel

George Mendle was a monk.

He noticed that characteristics in plants were passed on from one generation to the next.

His conclusions

  • Characteistics in a plant are determined by "Hereditary units".
  • Hereditary units are passed on from both parents.
  • Hereditary units can be both dominant and recessive.

Hereditary units are genes

19 of 25

Genetic diagrams

Alleles - Are different versions of the same gene.

Genotypes - The combinations of alleles for a characteristic.

Pheonotype - The feature or characteristic that is expressed.

Heterozyous - 2 different alleles.

Homozyous - 2 same alleles.


Recessive and dominant

Dominant - expressed if heterozygous.

20 of 25

Genetic disorders

Cystic fibrosis is caused by recessive allele.

It is a genetic disorder of the cell membrane, and resuts in the body producing a lot of thick sticky mucus.

For the child to have the disorder, both parents must be carriers or sufferers.

There is a 1 in 4 chance of the child having the disorder


Polydactyly is caused by a dominant allele.

This is a genetic disorder in which a baby is born with extra fingers or toes.

Only 1 parents needs to have the disorder.

There is a 50% chance of the child having the disorder

21 of 25

Screening for genetic disorders

A cell is removed from the embryo and its genes are analysed so that genetic disorders can be detected.

During IVF, it is possible to remove a cell from each embryo and analyse its genes.

Genetic disorders could be detectd this way, so embryos with good embryos would be implanted, while others would be destroyed.

For and against embryo screening

  • It wil help stop people suffering.
  • There are laws to stop it going to far.
  • During IVF, most embryos are destroyed anyway, so it just helps select the healthiest.
  • Treating disorders cost the goverment a lot of money.
  • There may be a time where everyone wants embryo screening so they can get the most desirable child.
  • The rejected embryos could have developed into humans.
  • It Implies that people with genetic problems are undesirable.
  • Screening is expensive.
22 of 25

Fossils and extinction

Fossils - Remains of plants and animals

1) From gradual replacement of minerals. Things such as bones are replaced by minerals as they decay forming a rock like substance.

2) From casts and impressions. The organism is buried in soft material, which later hardens and the organism decays leaving an impression.

3)Preservation where no decay.

  • In amber.
  • Glaciers.
  • Peat bogs. 
23 of 25

Fossils and extinction continued

Fossils show how many species have evolved.


Extinction happens if a specie envolve quickly enough.

Species become extinct because:

  • Enviroment changes too quickly.
  • New predators kill them.
  • New dieases.
  • New competitors.
  • Catastrophic events.
  • New species develop.
24 of 25


Speciciation is the development of a new species.

It occurs when population of the same species become so different that they can no longer breeed together to produce fertile offspring

Isolation and natural selection lead to speciation.

Isolation - Is where populations of a pecies are seperated.

  • Physical barriers. Floods, earthquakes...
  • Conditions on each side of the barrier will slightly be different. Leading to different characteristics.

The 2 groups will have become seperate species.

Species - Organisms that can breed together successfully

25 of 25


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all B2 Revision resources »