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