B2 Revision2012 Specification

All living things are made up of cells. The structures of different types of cells are related to their functions.

Part Function

Nucleus Contains genetic material, which controls the activities of the cell

Cytoplasm Most chemical processes take place here, controlled by enzymes

Cell membrane Controls the movement of substances into and out of the cell

Mitochondria Most energy is released by respiration here

Ribosomes Protein synthesis happens here

Parts of cells which animal and plant cells have in common:

Part Function

Cell wall Strengthens the cell

Chloroplasts Contain chlorophyll, which absorbs light energy for photosynthesis

Permanent vacuole

Filled with cell sap to help keep the cell turgid

Parts of cells which only plant and algal cells contain:

Bacteria are single celled organisms which contain:cytoplasm cell membrane cell wall

no distinct nucleus

Yeast is a single-celled organism, similar to bacteria, containing:

• Cytoplasm• Cell membrane • Cell wall

But, they also have a nucleus.

Cells may be specialised for a particular function. Their structure will allow them to carry this function out.

Cell Job Adaptations

Leaf cell:

absorbs light for photosynthesis lots of chloroplasts

Root hair cell:

absorbs water and mineral ions

finger like shape for large surface area

Sperm cell: fertilises an egg head contains an enzyme

to help penetrate egg

Red blood cell:

carries oxygen to the cells

thin outer membrane so oxygen diffuses easily

Substances have to pass through the cell membrane to get into or out of a cell.

Diffusion is a process that allows this to happen.

Particles diffuse from an area of high concentration to an area of low concentration.

Diffusion happens in our:

• Gut: digested food particles diffuse from the gut cavity to blood in the villus

• Lungs: oxygen moves from the alveoli into capillaries around the lungs

A tissue is a group of specialised cells that have a similar structure and function.

cells tissues organs organ systems

Tissue Function

Muscular tissue Contracts, bringing about movement

Glandular tissue Produces substances such as enzymes and hormones

Epithelial tissue Covers some parts of the body

Organ systems are groups of organs that carry out a particular function. For example, the digestive system:

Plants also usually contain differentiated cells, tissues and organs.

Leaves are adapted to absorb sunlight for photosynthesis

Three factors can limit the speed of photosynthesis: • light intensity• carbon dioxide concentration • temperature

Farmers can use their knowledge of limiting factors on photosynthesis to increase crop yields.

• Artificial light – extends time for photosynthesis• Heating – increases the rate of photosynthesis• Adding carbon dioxide (CO2) – increases the rate

Think about economics:The cost of providing extra lighting, heat and carbon dioxide has to be weighed against the increased crop yield and the extra income it will provide.

Tip: paraffin lamps provide light, heat and CO2!

Glucose is produced during photosynthesis and is used by the plant to make:• Cellulose - which strengthens the cell wall• Proteins - such as enzymes and chlorophyll

Glucose is stored by plants as starch, fats and oils.

Plants also need

nitrates to do this

The distribution of living organisms in a particular habitat may be affected by physical factors, such as:

• Temperature• Amount of light• Availability of water• Availability of nutrients• Availability of oxygen and carbon dioxide

Sampling: Quadrat• Square frame• Used to sample a small area• Samples chosen at random

Sampling: Along a Transect• Not random• Tape stretched between two points• Samples taken along the line using a quadrat• Shows how the distribution of organisms changes along

the line

Enzymes• Biological catalysts: speed up reactions.• Enzymes are protein molecules, and so are made up

of amino acids.

What happens at the active site?The enzyme is the lock, and the reactant is the key.

enzyme

reactant+

enzyme-reactant complex↔

products

enzyme+↔

+ ↔ ↔ +

Key phrases:Catalyst: A substance which changes the rate of a chemical reaction without being changed itself.

Enzyme: A biological catalyst.

Active site: Where substrates bind to an enzyme and undergo a chemical reaction.

Activation energy: The minimum amount of energy particles must have to be able to react.

+

Temperature and enzymes

Most enzymes in the human body work best at about 37oC.

Over 40oC most enzymes will stop working. The amino acids they are made form start to unravel and the shape of the active site changes.

We say that the enzyme is denatured.

pH and enzymesChanges in pH alter an enzyme’s shape.

The best pH for an enzyme depends on where it normally works.

For example, intestinal enzymes have an optimum pH of about 7.5 (alkaline).

Enzymes in the stomach have an optimum pH of about 2 (acidic).

AmylaseMade in the salivary glands, pancreas and small intestine.

It breaks down starch into sugars.

It works in the mouth and small intestine.

ProteaseMade in the stomach, pancreas and small intestine.

It breaks down protein into amino acids.

It works in the stomach and small intestine.

LipaseMade in the pancreas and small intestine.

It breaks down lipids (fats and oils) into fatty acids and glycerol.

It works in the small intestine.

The enzymes made in the pancreas and small intestine work best in alkaline conditions.

The liver produces bile which is released into the small intestine.

Bile neutralises the acid that was added to the food in the stomach.

Industry Function of enzymes

confectionery (sweets)

change glucose into fructose, which is sweeter so less is needed and is used in 'slimming' foods (isomerase).

baby food start off digestion of food (proteases and lipases)

biological detergent break down stains (proteases and lipases).

What do enzymes do for us?

Mitochondria:

tiny organelles found in most plant and animal cells.

Where the respiration reactions happen.

More active cells have more mitochondria.

Aerobic respiration (with oxygen)glucose + oxygen → carbon dioxide + water (+ energy)

When too little oxygen reaches the muscles during exercise, they use anaerobic respiration to obtain energy.

Anaerobic respiration (without oxygen)glucose → lactic acid (+ energy)

During exercise, the muscle cells respire more than they do at rest. This means that:

• Oxygen and glucose must be delivered to them more quickly

• Waste carbon dioxide must be removed more quickly

This is achieved by increasing:depth of breathingrate of breathing

heart rate

• Inside each cell is a nucleus.• Inside the human nucleus are 46 chromosomes (two

sets of 23, one set from Mum, one set from Dad).• Chromosomes are made from DNA.• A section of DNA is called a gene.

Where is the genetic information in a cell?

The genetic material is copiedThe cell divides once to form two genetically identical body cells

Mitosis is used for growth or to replace cells.

Mitosis

MeiosisForms gametes (sex cells).

The cell divides twice to form four gametes.

Each daughter cell contains half of the chromosomes of the original cell.

Stem CellsUnspecialised - they can become any type of cell in the human body.

As the cells of an embryo divide (by mitosis) and the embryo develops, the cells become differentiated.

Stem cells can be used in new treatments for Parkinson's disease and paralysis.

Can be harvested from inside embryos, umbilical cords and bone marrow.

There are social and ethical issues concerning the use of human embryonic stem cells.

Plant cellsMost plant cells stay unspecialised.

They can differentiate all through their lives.

Unspecialised cells are made at the stems and roots, where mitosis takes place almost constantly.

This makes it very easy to clone plants.

Alleles

Different forms of the same gene

For example, eye colour

Determining sex

Human body cells have 23 pairs of chromosomes in the nucleus.

One of these pairs controls the inheritance of gender - whether offspring are male or female.

Dominant or Recessive?Alleles are dominant or recessive.

Punnett SquaresShow the possible genotypes produced when two organisms breed.

Evolution

Fossils are the remains of organisms which died thousands or millions of years ago.

By looking at fossils, we can see that organisms have changed very slowly over time.

60 million years ago

1 million years ago

ProkaryotesEukaryotesMulticellular lifeAnimalsLand plantsMammalsHumans

Fossils form if an organism does not decay because:– little oxygen was present– poisonous gases killed of decay causing organisms – low temperature

Fossil FormationTrace or imprints are left behind by organisms.

Isle of Wight, UK

Fossil FormationHard parts of organism replaced by minerals.This is the most common type of fossil.

The fossil record is incomplete.Why?

• Early forms of life were soft bodied.• Fossilisation requires very specific conditions.• Many fossils are destroyed.• Many fossils have not been found yet.

Evolution by Natural SelectionIndividuals in a species show a wide range of variation.

This is because of differences in genes.

Individuals most suited to the environment are more likely to survive and reproduce.

The successful genes are then passed to the offspring in the next generation. Charles

Darwin

ExtinctionWhat causes organisms to become extinct?

• Competition• New predators• New diseases• Environmental changes

Why did the dinosaurs become extinct?

VolcanoesRocks formed by huge eruptions 65 million years ago can be found in India today.

Meteorite ImpactThe remains of a 180km-wide crater caused by a meteorite 65 million years ago can be found near Mexico.

DiseaseThis theory doesn’t explain why so many sea animals died at the same time.