Download B3_revision_notes

Year 11 Biology Revision Notes.
Module B3 Living and Growing.
Molecules of life
What’s in a cell?
Nucleus – contains genetic information, this is carried on chromosomes
Cell membrane – controls movement of substances in and out of the cell
Cytoplasm – where many chemical reactions happen
Mitochondria – cell respiration is carried out here. Energy is released from glucose in the presence
of oxygen.
DNA code
DNA is found in the nucleus. Forms structures called chromosomes. A section of a chromosome is
called a gene. Each gene is a code for making proteins. Our bodies need proteins to grow and make
proteins. Everyone has his or her unique DNA code.
DNA – double helix; complimentary base pairs (adenine – thymine; cytosine – guanine)
Need proteins for:
Growth, repairing new cells, building structures such as muscle, bone, skin, hormones, enzymes
Genetic code controls how enzymes are made in your cells, enzymes control chemical reactions in
the body, and will control your characteristics.
1
Year 11 Biology Revision Notes.
Module B3 Living and Growing.
History of DNA:
1953 Watson and Crick worked out DNA structure
Genes code for proteins. The double stranded DNA helix is in the nucleus, and contains the base
code which determines which proteins are made at the ribosomes. The DNA cannot leave the
nucleus so it’s base pairs separate and the strand unzips to form two single DNA strands. A copy is
made of part of one strand of the DNA, now called the messenger RNA. This single strand leaves the
nucleus and goes to the ribosome. The order of bases found in a section of DNA is called the base
code with each THREE bases code for an amino acid. At the ribosome the code is read and the
correct amino acids are put together in the correct order.
The sequence of the amino acids in the protein chain determines the shape that the protein will fold
up into.
Proteins determine your characteristics- The fact that proteins are folded in a specific way giving
them a specific shape, means that they have a particular function. Therefore the genes you inherit
determine what types of proteins your body makes and thus control your characteristics
Important proteins
Collagen
vessels
- found in skin, bones, tendons, ligaments, and walls of blood
Insulin- Is a protein hormone which is prodcued in the pancreas, travels to the liver and muscles
where is cuases blood sugar levels to be lowered
Haemoglobin- Is a carrier protein in red blood cells which carries oxygen
Enzymes – protein catalysts which speed up reactions in the body.
Different types of cell make different proteins- all our different types of cell have the same DNA but
they make different proteins. This is because they only have the genes switched on which results in
the production of specific enzymes (made of protein) e.g. pancreas cells only have genes swtiched
on which result in the production of insulin. Some genes do not make proteins but control the
switching on or off of other genes.
Enzymes
Enzymes are biological catalysts – they speed up a biological reaction.
2
Year 11 Biology Revision Notes.
Module B3 Living and Growing.
Involved in the following reaction: photosynthesis, respiration, protein synthesis
Each enzyme is specific to a substrate.
Enzymes can join substrate molecules together to make a larger molecule, or can break substrates
down into something smaller. (pictures are HT)
The substrate molecules are changed into product molecules.
Enzyme controlled reactions are affected by pH and temperature.
Optimum pH or temperature – the pH / temperature where the reaction works best.
Lock and key theory- each enzyme has a unique sequence of amino acids – therefore each enzyme
has a different shape. Within this shape is a structure called an active site. Only one type of
substrate can fit into the active site, this makes enzymes specific to a reaction. Once the substrate is
attached to the active site it is turned into a product. The enzyme is like a lock and the substrate is
like the key.
Low temperatures and enzymes: Low temperatures mean that the enzyme active site and the
substrate have less kinetic energy and so there are less collisions between them  the reaction is
slower
High temperatures and enzymes: There is a double in reaction rate for every 10 degrees Celsius
increases as there is more kinetic energy and the substrate collides more frequently with the
enzyme active sites.
Higher temperatures and enzymes-
Denaturing enzymes
If the shape of an enzyme changes it can no longer catalyse a reaction because the substrate can no
longer fit into the active site. The enzyme has become denatured.
Enzymes can be denatured by:

Extremes of pH

High temperatures
3
Year 11 Biology Revision Notes.
Module B3 Living and Growing.
Proteins and mutations
Gene mutation- is a change in a gene which can occur spontaneously (by itself) or by chemicals
such as tar in cigarettes, x-rays or UV light (sunlight)
HT- a mutation in a gene (a change in a base pair) results in a different protein being made which
cannot do its normal job
Harmful mutations- cause cells to keep dividing (cancer), different shaped haemoglobin (disease
called sickle cell anaemia)
Useful mutations – pale skin is a mutation (people all used to have dark skin) and pale skin lets
more light to make vitamin D (prevents rickets- soft bone disease) which is useful for people
who live in countries where the sun is not strong
Neutral mutations (not good or bad)-
Tongue rolling is due to a gene mutation
Energy and life processes

Energy is the ability to do work

Plants use light energy to make food and store it

Animals eat food containing stored energy
Building large molecules from smaller ones- plants make proteins out of long chains of amino
acids. Plants join sugar molecules they make in photosynthesis into starch (stored in the plant),
whereas animals join sugars to make glycogen (store energy in animals). Fatty acids and glycerol
are joined in animals and plants to form lipids.
Energy is needed for – muscle contraction or animals to move, and for animals such as birds and
mammals to keep their bodies warm. These animals need to eat more food to make heat energy
than cold blooded animals such as snakes that get heat from the sun to warm their body up.
Energy is released from food by a process in cells called RESPIRATION
OXYGEN + GLUCOSE  CARBON DIOXIDE + WATER (+ ENERGY)
C6H12O6 + 6O2  6CO2 + 6H2O (balance with 666- the sign of the devil)
4
Year 11 Biology Revision Notes.
Module B3 Living and Growing.
AEROBIC RESPIRATION HAPPENS ALL THE TIME IN PLANTS AND ANIMALS BUT ANAEROBIC
RESPIRATION (WITHOUT OXYGEN) ONLY HAPPENS WHEN THE CELLS ARE NOT GETTING ENOUGH
OXYGEN
Anaerobic respiration
Glucose  lactic acid (+ a little bit of energy, less than aerobic respiration)
Respiratory quotient is calculated
RQ = volume of carbon dioxide produced
volume of oxygen consumed
If the amount of carbon dioxide produced is the same as oxygen
used, the RQ value =1. If the cell is not getting enough oxygen, the RQ value will be greater than 1.
Rate of respiration increases during exercise as your muscle cells need to get more oxygen and
to get rid of more carbon dioxide
Respiration is controlled by enzymes so if you warm up before hard exercise, respiration will
happen faster. However, if there is increase anaerobic respiration more lactic acid is released,
pH goes down and this reduces the rate of respiration  muscles get tired and hurt
Oxygen debt- when you have exercised using a lot of anaerobic respiration lots of lactic acid is
produced. This needs to be broken down by oxygen, so when you finish exercising you carry on
breathing hard and fast to supply enough oxygen to break down the lactic acid  oxygen debt
Blood
Comprised of:

Plasma – a yellow liquid, adapted to transport dissolved substances such as water,
hormones, antibodies and waste products

Red blood cells – transport oxygen around the body. Red colour comes from haemoglobin.
Oxygen joins to the haemoglobin to form oxyhaemoglobin, which allows it to be transported
around the body. They do not have a nucleus – this leaves more room to carry oxygen.
They are disc-shaped and have a dent on both sides – this allows them to absorb a lot of
oxygen. They are very small so they can carry oxygen to all parts of the body.

White blood cells – defend the body against disease. They are adapted to change shape,
they can wrap around microbes and engulf them. They can squeeze through capillary walls
to reach microbes.

Platelets – help to clot the blood if we cut ourselves.
5
Year 11 Biology Revision Notes.
Module B3 Living and Growing.
Blood vessels
Blood is carried around the body in three different blood vessels.

Artery – thick muscular and elastic wall to help it withstand high blood pressure as the blood
leaves the heart.

Vein – large lumen (hole) to help blood flow at low pressure; valves stop blood from flowing
the wrong way.

Capillary – thin, permeable wall to allow exchange of material with body tissue
The Heart
Structure

Four chambers

Two atria – receive blood from the veins

Two ventricles – pump blood into arteries

Valves – bicuspid, tricuspid, semi-lunar valves – prevent the blood flowing backwards when
the heart relaxes and so maintain blood pressure.
Four key vessels

Right hand side:
o

vena cava, pulmonary artery
Left hand side:
o
pulmonary vein, aorta
Function

The heart pumps blood around the body. There are two sides to a heart.
6
Year 11 Biology Revision Notes.
Module B3 Living and Growing.

The right side pumps blood to the lungs

The left side pumps blood to the rest of the body

The blood leaves the heart in arteries where the pressure is high.

The blood returns to the heart at low pressure in the veins.
Double circulation- we are said to have a double circulatory system as blood goes through the heart
twice. Once on its way to the lungs, and once before it travels around the body
Divide and rule
Every day new cells are made. To do this the body carries out cell division. Cells divide whenever
the body needs to:

Grow

Replace worn out cells

Repair damaged tissue
Inside the nucleus of a human body cell there are 46 chromosomes. Humans have 23 pairs of
chromosomes. The chromosomes in a pair look the same and carry similar information. When a
cell has pairs of chromosomes it is called a diploid cell. During growth a type of cell division called
mitosis makes new cells. The new cells are exact copies and contain 23 pairs of chromosomes.
Mitosis
1. Cell resting
2. Each chromosome is copied, the single strand forms double-stranded “X” shape
3. Spindle forms, chromosomes arranged along equator
4. Chromosome single strands move to poles of cell
5. Two genetically identical cells are produced.
7
Year 11 Biology Revision Notes.
Module B3 Living and Growing.
6.
Human eggs and sperm

These are our sex cells or gametes. Gametes join during fertilisation. They are adapted to
carry out their jobs.

Much larger than the sperm because it contains food for the developing embryo

The nucleus of an egg contains genes which hold the instructions to make new cells
Egg
Sperm

Much smaller than the egg

Has a tail to help it move

Sperm also have a structure called an acrosome – this releases enzymes that digest the cell
membrane of an egg and allows the sperm inside.
Gametes have half a set of chromosomes called the haploid number. During fertilisation the
gametes join to form a zygote. The zygote is diploid and can develop into an embryo (baby).
When fertilisation takes place gametes from a male and female join. The resulting offspring have
genes from both parents. They are different to their parents – they are new individuals.
Reproduction using meiosis results in a lot of genetic variation within a species.
Meiosis
A special type of cell division that produces gametes. Gametes are made when diploid cells divide by
meiosis to produce haploid cells. Meiosis involves two cell divisions. First the chromosomes
separate then the chromosomes divide in the same way as mitosis
8
Year 11 Biology Revision Notes.
Module B3 Living and Growing.
Plant cells
Plant cells have the following components:

Nucleus –contains the genetic material (chromosomes)

Cytoplasm- where cells chemical reactions take place

Cell membrane- control what goes in and out of the cell

Vacuole – contains cell sap and provides support

Cell wall – provides support

Chloroplasts – absorb light energy for photosynthesis
Animal cells DO NOT have a cell wall, chloroplasts, or vacuoles
Animal cell and plant cell growth
For a fertilised egg to grow into an embryo and a foetus the cells need to divide and change so they
can carry out different jobs. Some cells turn into nerve cells and other cells may turn into bone cells.
This is called cell differentiation.
The cells of animals and plants cause them to grow in different ways.
Plant
Animal
Most growth is due to cells elongating (growing
longer) not dividing
Growth is due to cells dividing
Cell division only normally occurs at the tips of
shoots and roots
Cell division occurs all over the body
Many cells never lose the ability to differentiate
Most animal cells lose the ability to differentiate
very early on
9
Year 11 Biology Revision Notes.
Module B3 Living and Growing.
A few days after an egg is fertilised it contains a group of cells called stem cells. These all have the
same simple cell structure. They divide and then differentiate to form all the different specialised
cells in the body. As the embryo grows all the specialised cells form tissues and organs.
Some stem cells are found in the adult body. Bone marrow contains stem cells that turn into
different types of blood cells.
Scientists have found ways of making stem cells develop into other specialised cells in the hope of
replacing damaged cells. Ethically this can cause problems. People may object to stem cell research
because it can involve human embryos. Scientists use embryo stem cells because they are easier to
grow than adult stem cells.
Human growth
There are five main stages:
1. Infancy (rapid growth)
2. Childhood (slow steady rate)
3. Adolescence (puberty)- rapid growth
4. Adulthood (maturity)falls to zero
New genes for old
Selective breeding
Choose the animals and plants with the best characteristic and breed them to produce offspring that
have those characteristics. The selection and breeding process needs to be repeated for a number
of generations. This process could be used to breed cows that produce a lot of milk, chickens that
lay more eggs, crops that are resistant to certain diseases, crops that are resistant to flood/drought
Transferring genes
Scientists can take genes from one organism and put them into a different organism. These changes
are called genetic engineering or genetic modification (GM)
How genetic engineering works
1. Select the characteristic
2. Identify and isolate the gene
3. Insert the gene into the chromosome of a different organism
10
Year 11 Biology Revision Notes.
Module B3 Living and Growing.
4. Replicate (copy) the gene in the organism and produce the protein.
Enzymes are used to cut a gene out of an original chromosome and put it into a new chromosome.
Examples:
Insulin – a bacterium called E coli has been genetically engineered to make human insulin.
Vitamin A rice – rice is the main diet for many people living in Asian countries, it does not contain
vitamin A which is needed to prevent night blindness. Scientists have added the gene to make betacarotene from carrots to the rice plants. Humans eating the rice can then convert the beta-carotene
into vitamin A.
Some people are opposed to GM due to ethical reasons and have concerns of “playing God “with
nature.
Cloning
Clones are genetically identical. They have the same DNA as the original animal or plant. Identical
twins are natural clones – they have the same DNA.
Types of cloning:
Embryo transplantation
Sperm is collected from the prize bull; a prize cow is artificially inseminated with the sperm. When
the fertilised egg divides into an eight-cell embryo it is collected and split into four two-celled
embryos. Each embryo is implanted into a surrogate cow where it grows into a calf. All the calves
will be genetically identical to each other but not to their parents.
Nuclear transfer

Egg cell taken from sheep A and the nucleus is removed.
11
Year 11 Biology Revision Notes.
Module B3 Living and Growing.

An udder cell is taken from sheep B and the nucleus is removed.

The nucleus from sheep B is put into the egg cell of sheep A.

The egg cell is put into a sheep to grow.

The cell grows into a clone of sheep B (where the nucleus containing the genetic information
came from)
The importance of cloning

Organ supply for humans

Cloning of human embryos to provide stem cells
Risks

Low success rate

Moral / ethical issues

Complications / early death of clones
Benefits

Cloned pigs could make up a shortage in transplant organs

Diseases could be cured using embryonic stem cells
Asexual reproduction in plants
Plants that can do it naturally:

Potato plants – tuber

Strawberries – runner

Spider plants – plantlets
Strawberry plants has long runners and at the end baby plants grow (genetically
identical to the parents plantas there is only one parent)
12
Year 11 Biology Revision Notes.
Module B3 Living and Growing.
New plants from old
How? – take cuttings. You cut off a stem or a root from a plant and put it into soil and it will grow
into an identical plant to the one you cut it from
Advantages of cloning plants

All the plants are genetically identical

Cloning is quite. a quick process in comparison to growing plants from seeds

Cloning enables growers to produce plants that are difficult to grow from seed such as bananas
Disadvantages

The plants are all genetically identical. If the environment changes or a disease breaks out it is
unlikely any of the plants will survive.

Cloning plants over the years has resulted in very little genetic variation
Tissue culture
Plants can be cloned using tissue culture. This must be carried out using aseptic technique
1. Plants with desired characteristics are chosen
2. A large number of small pieces of tissue are taken from the parent plant
3. They are put into sterile test tubes that contain the growth medium
4. The tissue pieces are left in suitable conditions to grow into plants
13