Diffusion—the spreading out of particles

The movement of particles from an area of high concentration to an area of low con-

centration. Down a concentration gradient. The greater the difference in concentra-

tion in two cells the faster the rate of diffusion.

(involves the movement of particles, and therefore only takes place in liquids and gas-

es)

Plant Example

Carbon dioxide diffuses into a leaf through the stomata.

Minerals and water diffuse into the plant through the roots.

Animal Example

Food molecules diffuse into the blood stream in the small intestine.

Water molecule diffuse into the blood stream in the large intestine.

Oxygen molecules diffuse into the bloodstream in the lungs.

Cells

You need to be able to identify and know

the functions of the following parts of

cells.

nucleus – controls the activities of the cell

cytoplasm – where the chemical reactions

take place

cell membrane – controls the movement

of substances into and out of the cell

mitochondria – release energy (this is

where aerobic respiration occurs)

ribosomes – where protein are made

(protein synthesis)

cell wall – strengthens the cell

chloroplasts – absorb light energy to do

photosynthesis. Chloroplasts contain chlo-

rophyll which is a green substance.

Cell Wall

Cell Membrane

Cytoplasm

Nucleus

DNA free in cell (no nucleus)

Vacuole

Bacterial Cell Yeast Cell

Specialised Cells

Some cells are specialised to carry out a particular function.

Root Hair Cell

Large surface area to increase the uptake

of water and nutrients

Sperm Cell

Have lots of mitochondria to release lots of

energy so the sperm can swim towards the egg.

Fat Cell

Fat cells can expand to fill with fat. They have a small

amount of cytoplasm to allow more space for fat.

Tissues, organs and organ systems

A group of cells that are specialised and come together for a spe-

cific function is known as tissue. Examples of tissues are:

Muscular tissue which can contract to bring about move-

ment. The cells have lots of mitochondria to release lots of

energy.

Glandular tissue, which can produce substances like en-

zymes and hormones

Epithelial tissue which covers some parts of the body

Organs are made up of different types of tissue. For example, the

stomach, (which is an organ) contains the following tissues:

Muscular tissue—to churn the contents of the stomach

Glandular tissue—to produce digestive juices

Epithelial tissue—to cover the outside and inside of the

stomach

Organs that work together to achieve a specific function is know as

an organ system. Examples of organ systems are:

The digestive system

The circulatory system

The respiratory system.

A group of organ systems working together form an organism.

Multicellular organisms have many different cells which are spe-

cialised for a particular function, an advantage over single-celled

organisms.

Some processes are easier for single-celled organisms, for example

oxygen can easily diffuse into a single cell.

Multicellular organisms need a transport system to bring oxygen to

every cell in their body. They also have specialised tissues that are

adapted for allowing things to move in and out of the body quickly.

Functions of the digestive system:

A system is a group of organs that

perform a particular function.

The function of the digestive system

is to break down the food you eat so

the food molecules can enter the

blood.

Each organ in the system has an im-

portant role to play to ensure that

this happens. See the diagram on the

left.

The digestive system includes:

Glands such as the pancreas

and salivary glands

The stomach and small

intestine where digestion occurs

The liver which produces bile

The small intestine where the

absorption of soluble food occurs

The large intestine, where

water is absorbed from the undigest-

ed food, producing faeces.

Enzymes

Enzymes are biological catalysts which speed up the rate of reactions. Enzymes are made from

PROTEINS.

Proteins: proteins are made up of AMINO ACIDS.

Factors Affecting Enzymes

1. Temperature— as the temperature increases the

rate of the reaction increases until an opti-

mum temperature is reached. If the tempera-

ture gets too hot the enzyme is DENATURED

which changes the SHAPE of the ACTIVE SITE.

This means the SUBSTRATE will no longer fit the enzyme and cannot be broken down.

2. pH—different enzymes work at different pH’s. The stomach produces HYDROCHLORIC

ACID to KILL BACTERIA in the food which makes the stomach acidic. Protease works

best in acidic conditions but lipase and amylase cannot work in acidic conditions. They

work best in alkaline conditions.

Enzymes in Digestion

Enzymes are released from glands.

They break down large molecules into smaller ones so that they can

be absorbed by the small intestine into the blood stream.

Bile

The LIVER produces bile which is then stored in the gall bladder. It is added to the food after

It leaves the stomach to neutralise the stomach acid. It is important to neutralise the acid so

that amylase and lipase can break down food in the small intestine.

Enzyme Enzyme made ….. Where it breaks food down…. What it breaks down…..

Amylase Salivary glands, pancreas, small

intestine

Mouth and small intestine Starch into sugars

Protease Stomach, pancreas, small intes-

tine

Stomach and small intestine Protein into amino acids

Lipase Pancreas and small intestine Small intestine Lipids into fatty acids and glycerol

Enzymes in the Home and Industry

Home:

Washing powder contains protease and lipase to break down fat and protein

stains on clothing.

Washing powders with enzymes in (biological detergents) are more effective

at lower temperatures and therefore you can save energy and money.

Industry:

Proteases are used to pre-digest proteins in baby foods.

Carbohydrases are used to convert starch into sugar syrup

Isomerase is used to convert glucose syrup into fructose syrup. Fructose is

sweeter and therefore less can be used in slimming products.

NEGATIVES: Enzymes cannot be used at high temperatures because they are

DENATURED. Enzymes are also COSTLY to produce.

Sampling 2 Areas to Compare Them

As scientists we may want to study the distribution of organisms in different areas.

Q. Describe how students could use a quadrat to estimate the numbers of different plants

growing on a field.

Place a quadrat on the field randomly. This avoids bias.

This could be done by throwing the quadrat or using a random number generator to

calculate coordinates.

Count the plants within the quadrat.

Repeat the process above

Then calculate a mean

If they wanted to compare two fields such as St Mark’s football field and HAM’s they would

do the same as above on each field and then compare the amount of plant being looked at.

The green dots show the randomly sampled areas to count. In

total this is 15 squares. The total area is 48.

To improve the estimate simply increase the sample size so in-

stead of counting 15 quadrats count 20 or 25 instead.

Only an estimate is being produced because the whole area/field

is not being counted.

Extra Info

If sampling the cover of 1 species only count a quadrat

is it is more than half full. Eg I would count quadrats

1, 2,4 and 5 but not count quadrat 3 and 6.

To improve the reproducibility and validity of the

estimates use a larger sample size eg more quadrats

or bigger quadrats.

Factors Affecting Organisms

Organisms (living things such as plants and animals) are affected by many physical factors:

Temperature

Availability of nutrients

Amount of light

Availability of water

Availability of oxygen and carbon dioxide

Without the things above, we could not survive. The more plants have of the things they

1 2 3

4 5 6

Sampling 1 Area Using a Line Transect

A line transect is simply a tape measure placed across an area.

Q. Describe how a line transect could be set up to estimate the numbers of different plants

growing at different places across a river.

Place a tape measure across the river to produce a transect

Place quadrats at regular intervals along the tape measure

Count the cover/percentage of plants in each quadrat

Repeat the process by placing the transect at different places along the stream. At

random or regular intervals

This

could be

done in

any en-

vironment such as a forest, a field or a pond.

Plants

Like all organisms, plants are made up of cells, which in turn form

tissues, which come together to form organs, then organ systems

and finally the complete organisms. The organs in a plant are made

up of tissues. Plant organs include stems, roots and leaves.

The whole plant is covered in a layer of epidermis tissue. The epi-

dermal tissue on the lower surface of the leaf has little holes called

stomata. These allow gases to diffuse in and out of the leaf.

Most of the cells in a leaf are mesophyll cells. This is where photo-

synthesis takes place.

Xylem and phloem tubes run through the entire plant. These are

tubes which make up the plant’s transport system: xylem carries

water from the roots to the leaves and sugars are transported

Photosynthesis

The word equation for photosynthesis is:

Energy from sunlight

Carbon dioxide + water glucose + oxygen.

The carbon dioxide comes from the air and diffuses into leaves

through the stomata. Water comes from the soil and enters by

diffusion into the roots. Glucose and oxygen are the products;

oxygen diffuses out of leaves as a by-product. Light energy is

absorbed by chlorophyll found in the chloroplasts of plant cells. Chlorophyll is green and is essential for pho-

tosynthesis.

Plants carry out photosynthesis to produce glucose for respiration. Plants carry out respiration just the same

as humans; they need energy for cell processes too. However, plants don’t use up all the glucose so they

store some of it as starch, which is insoluble. The glucose is also used:

To produce fats or oils as an energy store

To produce cellulose, which strengthens the cell walls

To produce proteins—but to make proteins, plants also need nitrates, which have to be absorbed

from the soil.

Limiting factors

This figure shows that as the light intensity increases , the rate of photosynthesis also increases. Between A and B, we say light is

a limiting factor for photosynthesis, as you can still increase the light intensity and see the rate of photosynthesis go up. However,

there comes a point where the rate of photosynthesis does not increase anymore, even when the plant is getting more light

(where the graph has levelled off). This is because something else is acting as a limiting factor, for instance, carbon dioxide concen-

tration.

Increasing the carbon dioxide concentration, then, will increase the rate of photosynthesis. However, eventually the graph levels off again, because some-

thing else (light intensity, or maybe temperature) is acting as a limiting factor.

Increasing the temperature tends to increase the rate of photosynthesis, but if it gets too hot, then enzymes denature and the rate drops again. See graph.

Growing crops in a greenhouse gives the grower a lot of control over the conditions in which plants live. A grower may be able to produce more tomatoes

quickly if they heat the greenhouse, but the cost of fuel might outweigh the increase in what they are paid for the tomatoes.

Aerobic Respiration

Aerobic respiration takes place continuously (all the time) in

plants and animals. Yes, plants do mainly photosynthesis

to make their food but they also do respiration to release

energy.

During AEROBIC RESPIRATION, cells use oxygen and glucose to

release energy—as shown in the equation to the right.

Most of the reactions take place in the mitochondria, con-

trolled by enzymes.

The energy release is then used in many different ways in the

body.

Respiration

Aerobic Respiration:

GLUCOSE + OXYGEN CARBON DIOXIDE + WATER (+ENERGY)

Anaerobic Respiration

During exercise there is a greater demand for energy. If

muscles can’t get enough oxygen they use anaerobic respira-

tion to release energy.

This involves the incomplete breakdown of glucose which

produces lactic acid.

Unfortunately anaerobic oxygen releases LESS ENERGY! Anaerobic Respiration:

GLUCOSE CARBON DIOXIDE + LACTIC ACID (+ENERGY)

The energy produced during respiration is used:

to build larger molecules from smaller ones (e.g. in

plants, to build amino acids which can then be joined to

make proteins)

to allow muscles to contract

to maintain a constant body temperature (in warm-

Exercise—flex those muscles

During exercise,:

the heart rate increases

the rate and depth of breathing

increases.

These changes increase blood flow to muscles, so they can

be supplied with MORE glucose and oxygen and carbon

dioxide can be carried away.

Muscles can store glucose as glycogen. Glycogen can be

converted back to glucose to be used during exercise. Muscle Fatigue

Build up of lactic acid is one cause of muscle fatigue

(muscles stop contracting efficiently). This happens

after long periods of vigorous exercise.

Lactic acid is re-

moved from muscles

by the flow of blood.

Aerobic Respiration Anaerobic Respiration

More energy released Less energy released

Oxygen required No oxygen required

Carbon dioxide and water

produced

Lactic acid produced

Genetics and DNA

Organisms produced by sexual reproduction (like you) are genetically unique

because they inherit half of their DNA from each parent when the gametes fuse

at fertilisation.

In humans, there are 23 pairs of chromosomes (46 in total, 23 from each par-

ent). One pair of chromosomes determines your sex. The combination XY (as

shown) is found in males; in females, the combination in XX. So the diagram

shows a male’s set of chromosomes.

Mendel investigated inheritance

This monk realised that some factors are inherited, and they don’t necessarily add up to give the

offspring a certain characteristic. For example, as the diagram shows, if a tall pea plant is bred with a

short one, all the offspring are tall, rather than all being somewhere in between, as he might have

expected. He didn’t know about dominant or recessive alleles, but later work proved that his result

were due to inheritance of certain alleles.

His work wasn’t initially accepted because:

Insufficient evidence

He was only a monk and scientists

didn’t read his papers

The method of inheritance (DNA and genes) were unknown

Cell Division

There are two types of cell division:

Mitosis: for growth and replacement od cells. The new cell is genetically identi-

cal to the parent cell. The DNA replicates and then cell division occurs.

Meiosis: for the production of gametes. Higher Tier only: copies of the genetic

information are made and then the cell divides twice to form 4 gametes. Each

gametes contains only a single set of chromosomes)

Key Term Meaning

Gene A small section of DNA that controls a characteristic.

DNA A molecule with a double helix structure; chromosomes are

made from this

Chromosome One molecule of DNA; appear in pairs in cells. Contains ge-

netic information.

Allele A form/version of a gene; alleles can be dominant or reces-

sive

DNA

fingerprinting

Process of identifying individuals using their DNA, since eve-

ryone’s DNA is unique (except identical twins)

Homozygous

(higher tier)

An organism has 2 of the same allele for a characteristic eg

FF or Ff for cystic fibrosis

Heterozygous

(higher tier)

An organism has 2 different alleles for a characteristic eg Ff

for cystic fibrosis

Pheneotype

(higher tier)

The physical characteristic of an organism. For example blue

eyes or brown hair.

Geneotype

(higher tier)

The combination of alleles for a characteristic. For example

Bb or BB.

Passing on alleles

Because we have two copies of every gene (one from each parent), when gam-

etes (sex cells) are made during meiosis, each gamete only gets one copy of the

gene, or one allele. This is what you put on the Punnet square to decide the

chance of inheriting each combination of alleles. NB gametes are the only types

of cell with just one set of chromosomes; all other body cells have two sets.

Genetic Crosses

With Disease : Without Disease

1:3

Ff:FF Ff Ff

Inherited Conditions: Polydactyly

The condition involves additional fingers and toes. It is

caused by a dominant allele, so even if only one parent

has it, the children can inherit the disease, as the dia-

gram shows.

Inherited Conditions: Cystic Fibrosis

This condition (production of thick, sticky mucus in the lungs and

digestive system) is caused by a recessive allele. This means that

both parents must have a copy of the allele for a child to inherit

the disease.

It is a disease of the cell membranes.

Parent’s gametes

(both are carriers)

Par

ent’

s ga

met

es

(bo

th a

re c

arr

iers

)

Embryo Screening—embryos are screened to see if they contain genes which

will cause an inherited disease.

Advantages

Good chance of having a child without the disorder

A child with the disorder could be expensive to raise

Disadvantages

Operation dangers for mother

Embryo could be damaged during screening

Expensive

Right to life—ethical issues with destroying embryos

Stem Cells

A cell which has become specialised is said to be differentiated. For example a muscle cell or a nerve

cell. If it divides by mitosis to make a new cell it can only make the same kind of cell. Muscle makes

muscles and nerve makes nerve.

Most of our cells differentiate early on but plant cells retain the ability to differentiate throughout

their life.

Stem cell are unspecialised cells and have the ability to become any kind of cell. This is why they are

used in medicine to treat conditions such as paralysis: they have the ability to become any kind of cell.

We find stem cells in adult bone marrow (the centre of the bone).

Pros of using embryo stem cells in research and treatment:

Can treat a wide variety of diseases

Painless for embryos

Cons of using embryo stem cells in research and treatment

Death of embryo

The embryo has right—could not be asked

Collecting and growing cells can be expensive

Fossils

We know about species that used to

live on Earth because some of them

left FOSSILS.

Fossils are the remains of dead or-

ganisms found in rocks, and here’s

how they form:

After they die, they are covered with sediment or mud

The soft parts of their body (e.g. skin) decay

The bones don’t decay

Over a long period of time, the bones are replaced by

minerals in the sediment

Some fossils are just traces of organisms rather than their bod-

ies—for instance, their tracks or poo. Dead organisms can also

be preserved if they can’t decay—if there are no microorgan-

isms, for example if the dead organism gets frozen in ice.

Fossils show how life has changed on Earth over time. For in-

stance, fossils act as a record of organisms that are now extinct.

The fossil record is not complete, because not that many dead

organisms form fossils. Also, the early organisms on Earth had

soft bodies, so they didn’t usually leave fossils; they usually just

decayed. Any fossils that were left have mostly been destroyed

thanks to geological activity like earthquakes.

Extinction

Most organisms that have lived on Earth are now extinct, which means all the individuals of a species have died out.

Sometimes lots of organisms die out all at once. This is called MASS EXTINCTION.

There have been five mass extinctions on Earth since life emerged, where massive natural disasters wiped out most

species of living thing on the planet. Mass extinctions could be caused by:

Natural disasters, such as meteors hitting the Earth or massive volcanic eruptions

Climate change

Individual species can become extinct without such drastic events happening. For instance, extinction of a species can

happen because of:

Long term changes to the environment (the organism can’t adapt to these

changes)

New predators in their habitat

New diseases

New competitors (e.g. for food), that are more successful Extinct. Sorry.

Forming New Species

All living species on Earth are descended from one single ancestral (as in, ancestor of) species. The fossil and DNA evidence sup-

port this idea, but since the fossils are rare and no humans were there to see it, we don’t really know what it was like.

However, we do know that new species arise from existing species. This happens when the population of a particular species is

split up, into two or more smaller populations. This is called isolation, and can happen due to a geographical barrier, such as a

mountain range or strip of land splitting the ocean—see the example.

Old and New Species

These two species of fish formed when the

ancestor species was split into two popula-

tions (isolation occurred) when North and

South America joined up at Panama.

Higher Tier Only: you should explain that

when isolation occurs, new species can form

because:

There is genetic variation in each

population

Natural selection occurs in each

population, but different alleles are

favourable in each population

Speciation occurs, where successful

interbreeding is no longer possible