B3- Living and Growing



Animal Cell Structure

  • Nucleus: Contains DNA in the form of chromosome
  • Cell Membrane: holds the cell together and controls what goes in and out
  • Ribosome: where proteins are synthesised
  • Cytoplasm: gel-like substance where most of the cell's chemcial reactions happen
  • Mitochrondria: where most of respiratopm takes place, it provides energy for cell process. Cells that need lots of energy contain alot of mitochondira

Plant Cells have a Nucleus, Cytoplasm, Cell Membrane

  • Chloroplast: where photosynthesis happens
  • Cell Wall: made of cellulose, it supports the cell
  • Vaucole: a relatively large stucture that contains cell sap

Bacteria Cells have a Cytoplasm, Cell Membrane, Cell Wall

  • They don't have chloroplasts or mitochondria and they don't have a true nucleus
1 of 18


  • Chromosomes are long molecules of coiled up DNA which is divided into short sections called genes.
  • DNA is a double helix and each of the strands is made up of groups called nucliotides
  • Each nucleotide contains a small molecule called a base
  • The four bases are A, T, G, C
  • Each base form cross links to a base on the other strand which keeps them wound together
  • T always pairs up with A and G always pairs up with C COMPLEMENTARY BASE-PAIRING

Watson and Crick were the first scientists to build a model of DNA, X-Ray data showed that DNA is a double pairing which showed that bases are in pairs

  • DNA can replicate itself so every time a cell divides a new cell still has the full amount of DNA
  • DNA double helix unzips to form two single stranfd
  • New nucleotides then join on using complementary-base pairing which makes an exact copy of the DNA
  • The result is two double-stranded molecules of DNA
2 of 18

Protein Synthesis

  • DNA controls the production of proteins in a cell
  • The section of DNA that codes for a particular protein is called a gene
  • Proteins are made up of chains of molecules called amino acids
  • This gives each protein a different shape which means each protein can have a different function
  • The order of the bases in a gene decides the order of amino acids in a protein
  • Each amino acid is coded by a sequence of three bases
  • The amino acids are joined together to make proteins following the order of the bases in a gene
  • Each gene contains a different sequence of bases which allows it to code for a unique protein

Proteins are made in the cytoplasm by tiny structures called ribosomes and to make proteins, ribosomes use the code in DNA. DNA is found in the nucleus and the cell needs to get the code from the DNA to the ribosome. This is done by a molecule called mRNA which is made by copying the DNA. It acts as a messenger between the DNA and the ribosome

3 of 18

Functions of Proteins

  • Enzymes- control cell reactions
  • Carrier Molecules- used to transport smaller molecules, e.g. haemoglobin binds to oxygen molecules and is then transported around the body
  • Hormones- used to carry messages around the body, e.g. insulin is a hormone released into the body by the pancreas
  • Structural Protein- are physically strong, e.g. collagen is a protein that strengthens connective tissue

Enzymes contol cell reactions. These reactions need to be carefully controlled to get the right amounts of substances and you can usually do it by raising a temperature but also the unwanted ones, its cells will start to get damaged. Living things produce enzymes which reduce the need for high temperature and we only have enzymes to speed up reactions. Each biological reaction has its own enzyme designed for it

Chemical reactions are split apart or joined together, the substrate is the molecule changed. Every enzyme has an active site where it joins on to its substrate to catalyse the reaction

4 of 18

More on Enzymes

If a reactions gets too hot some of the bonds of the enzyme will break and it will lose it shape and the active site won't fit the substrate anymore so it can't catalyse the reaction and it stops. The enzyme is now denatured. Each enzyme has its own optimum temperature when the reaction goes fastest which for humans is around 37'c.

Enzymes like the right pH too!!!! If it is too high or too low it interferes with the bonds holding the enzyme together which changes the shape of the active site and it denatures. Enzymes are often neutral at pH 7 but pepsin which breaks down proteins in the stomach works best with around pH 2.

The Q10 value of a reaction shows how much the rate changes when the temperature is raied 10'c.

Q10= rate at higher temperature

          rate at lower temperature

5 of 18


A mutation is a change in the DNA base sequence which could stop the production

  • Producing the wrong protein or no protein can be a disaster and if it occurs in the reproductive cells then the offspring might get the abnormality too. If it is in the body cells then it can start to multiply in an uncontrolled way. This is cancer
  • Occasionaly it can benefit us as it can give a survival advantage to the offspring and this is how natural selection and evolution work

Radiation and Chemicals

  • Ionising radiation including X-Rays and ultraviolet light increases the chance of mutation
  • Certain chemicals which are known to cause mutations are mutagens. If mutagens produce cancer then the chemicals are often called carcinogens. Cigarrette smoke contains this
6 of 18

Multiplying Cells

  • Being multicellular means you can be bigger, you can have cell differentiation and they are more complex so can have specialised organ systems.
  • However, being multicellular means you have to have specalist organ systems that have a nervous system, a circulatory system, and a respiratory system

MITOSIS is when the cell reproduces itself by splitting to form two identical offspring

This happens when you want identical cells e.g. when you want to replace worn out cells

  • Before it starts the DNA is replicated
  • Then at the beginning the DNA coils into double-armed chromosomes which are exact copies of eachother
  • The chromosome line up at the centre of the cell and then divide as cell fibres pull them apart, the two arms of each chromoome go to opposite poles and membranes form around these
  • The cytoplasm divides and you get two new cells containing exactly the same genetic material
  • AND THATS MITOSIS!!!! You end up with two new cells that are genetically identical
7 of 18

Meiosis, Gametes and Fertilisation

  • Meiosis creates gametes which are formed in the ovaries and testes and they are sex cells
  • The DNA replicates itself and curls up to form double-armed chromosomes
  • They arrange themselves into pairs, humans have 23 pairs. Both chromosomes contain information about the same feature one from mom and one from dad
  • The pairs split up and move to opposite poles of the cell, in each of the two new cells there are no pairs at all just the 23 chromosomes. Each new cell ends up with a micture
  • The second division is each chromosome splits in hald and one arm ends up in each cell
  • You have ended up with four new cells. These cells are genetically different from eachother because the chromosomes get all shuffled up and each gamete gets half of them at random

At fertilisation male and female gamete combine to form a diploid cell. The zygote characteristics are controlle by the combination of genes on its chromosome. Since it will have inherited chromosomes from two parents it will show features from both parents

A sperm's function is to transport male DNA to the females egg. Sperm are small and have long tails so they can swim to the egg. Sperm have lots of mitchondira to provide energy needed to swin and they have an acrosome which release enzymes they need to digest through the egg

8 of 18

Stem Cells, Differentiation and Growth

Animals tend to grow until they have reached a finite size, plants grow continuosly. In animals growth happens through cell division and plants its due to cell elongation

Differentiation is the process by which a cell changes to become specialised for its job. Some are undifferentiated as they can turn into different types of cells depending on the instructions they are given. These are called STEM CELLS. These are found in human embryos and they are found in bone arrow by they aren't as versatile as embryonic one

They can be used to cure disease like blood disorders through bone marrow transplant. Very early human embryos contain these and they can be extracted and grow them

Some people are against this research becase it shouldn't be used as it is a potential human life. Others think curing ones who already exist and are suffering is more important. Ones used in this are usually unwated ones from fertility clinics which would probably be otherwise destroyed. In the UK this is allowed but it is under strict guidelines

9 of 18


  • There are different ways to measure growth:
  • Length: Just measure the length, this is easy to meausre but it doesn't tell us the width or diameter
  • Wet Mass: Weigh the plant or animal, this is easy to measure but it is very changeable if it is just eaten or have a full bladder
  • Dry Mass: Dry out the organism before weighing it, it is not affected by the amount of water in a plant or anumal or how much the organism has eaten but you have to kill the organism first
  • Infancy= roughly the first two years of life, rapid growth
  • Childhood= period between infancy and puperty, steady growth
  • Adolescence= begins with puberty and continues until development, rapid growth
  • Maturity/Adulthood= period between adolescence and old age, growth stops
  • Old age= usually considered to be between age 65 and death

Organisms don't grow evenly at different times the body will grow at different rates. When a baby is developing in the womb the brain grows at a greater rate than the rest of the body because a large well-developed brain gives them a survival advantage

10 of 18


Respiration goes on in every cell in the body, it releases energy from glucose. The energy can't be used directly by cells so it is used to make ATP which acts as an energy source for many cell processes and transports it to where it is needed. It is controlled by enzymes so it is affecte by temperature and pH.

  • Aerobic Respiration needs Oxygen.
  • Glucose + Oxygen -> Carbon Dioxide + Water + ATP
  • C6H12O6 + 6O2 -> 6CO2 + 6H2O + ATP
  • Anaerobic respiration doesn't use oxygen and it is when we do vigorous exercise and our body cannot supply enough oxygen to our muscles. The glucose is partially broken down and lactic acid is produced which gets painful
  • We have an oxygen debt because you need extra oxygen to break down all the latic acid that is built up in our muscles which means we are breathing hard after we stop exercising, the lactic acid has to be carried to our liver to be broken down
11 of 18

Functions of the Blood

  • Plasma is the liquid bit of blood
  • Red blood cells, white bood cells and platelets
  • Water
  • Digested food products like glucose and amino acids
  • Carbon Dioxide from the body cells to the lungs
  • Urea from the liver to the kidneys
  • Hormone which act as chemical messengers
  • Antibodies which are proteins involved in the body's immune response

Red Blood Cells Carry Oxygen

  • They are small and have a biconcave shape which gives it a large surface area for absorbing and releasing oxygen.
  • They contain haemoglobin which is what gives the blood its colour and it contains alot of iron. Haemoglobin combines with oxygen to become oxyhaemoglobin. In tissues the reverse happens to relase oxygen to the cells. Red blood cells don't have a nucleus and this frees up more space for haemoglobin so they can carry more oxygen. They are very felxible which means they can pass through tiny capillaries
12 of 18

Blood Vessels

Blood Vessles are designed for their function!!!

  • Arteries= carry blood away from the heart
  • Capillaries= involved in the exchange of materials at the tissues
  • Veins= these carry blood to the heart

Arteries: The heart pumps blood at high pressure so the artery walls are strong and elastic. The walls are thick compared to the size of the hole down the middle (lumen). They contained thick layers of muscle to make them strong

Capillaries= Are really tiny and they carry blood really close to every cell in the body to exchange substances with them, they have permeabke walls so the substances can diffuse in and out. They supply food and oxygen and take away CO2. Their walls are usually one cell thick which increases the rate of diffusion by decreasing the distance over which it occurs

Veins= The blood is at lower pressire in the veins so the walls don't need to be as thick but they have a bigger lumen to help blood flow despite the lower pressure. They also have valves to help the blood flow in the right direction

13 of 18

Selective Breeding

Selective Breeding is when humans breed plants or animals to get the best characteristics that they want for example the maximum yield of meat, milk, good disease or something like temperament and speed.

The basic process is:

  • From your existing stock select the ones which have the best characteristics
  • Breed them with eachother
  • Select the best of the offspring and breed them together
  • Continue this over several generations

Reduction in the gene pool

It reduces the gene pool because the number of different alleles are reduced because the farmer keeps breeding from the best animals which are all closely related- inbreeding. It can cause health problems such as genetic disorders as the gene pool is limited and the genes are recessive. If a new disease appears then it is because there is no variation in the population and the stock are so closely related that if one is to die of a disease then they are also likely to die of it

14 of 18

Genetic Engineering

  • 1) First the gene is selected
  • 2) It is then cut from the DNA sequence using enzymes and is isolated
  • 3) The useful gene is inserted into the DNA of another organism
  • 4) The organism then replicates and soon there are loads of similar organisms

In some parts of the World it is heavily dependant on rice and Vitamin A deficiency can be a problem. Because rice doesn't include much of this genetic engineering has allowed scientists to take a gene from carrot plants and put it into rice plants

The gene for human insulin prodution has been put into bacteria which are cultered a fermenter and then it is simply extracted from the medium as they produce it

Some plants have resistants to herbicides, frost damage and disease so with genetic engineering we can cut out the gene responsible and stick it into the useful plants like crops

15 of 18

Gene Therapy and Cloning Animals

Gene therapy can be used to cure genetic disorders. It involves altering a person's genes to cure genetic disorders. One type is changing the gene in body cells so cystic fibrosis affects the lungs so therapy would target the cells in the lining of the lungs. This wouldn't affect there gametes so their offspring could still inherit it. The other type is changing the genes in the gametes so every cell of any offspring will be affected by therapy and they won't suffer from the disorder. It is controversial though, for example it could have consequences and cause a new set of problems  and there are fears that the kind of therapy could lead to designer babies

Cloning is making a genetically identical offspring. Dolly was produed using a method called nuclear transfer which involves placing the nucleus of a body cell into an egg cell.

  • The nucleus of the sheep was removed
  • Another nucleus was inserted into its place, which was a diploid cell from an udder cell of the different sheep
  • The cell was given an electric shock so that it staryed dividing by mitosis
  • The embryo was implanted into the uterus of a surrogate mother sheep
  • The result was Dolly, a clone of a sheep where the udder cell came from
16 of 18

Risks of Cloning

There are Benefits and Risks involved in cloning

  • Cloning allows us to mass produce animals with desirable characteristics, Researches have managed to transfer human genes that produce things like the blood clotting agent which is used to treat haemophilia
  • Animals like pigs have organs suitable for transplantation into humans could be developed so there is a constant supply of organs
  • Human embryos could be produced by cloning adult cells and they could be used in stem cells for stem cell therapy 
  • There is some evidence that cloned animals might not be as healthy as normal ones
  • Cloning is a new science and it might have consequences that we're not yet aware of

Some people are worried that there would be alot of surrogate pregnancies with a high rate of misscarriage and stillbirth. Clones of other mammals have been unhealthy and often die early and even if one were to be produced it might be psychologically damaged knowing it was a clone of someone else

17 of 18

Cloning Plants

Cloning Plants is by taking cuttings of good parent plants then planting them to reproduce genetically identical copies. This is easier than cloning animals because many plant cells keep their ability to differentiate.

Commercial Cloning

  • First you choose the plant you want to clone based on its characteristics
  • You remove several small pieces of tissue from the parent plants, getting the best results from fast-growing roots and short tips
  • Grow the tissue in a growth medium containing nutrients and growth hormones which is done by aseptic conditions to prevet growth of microbes that could harm the plants
  • As the tissues produce shoots and roots they can be moved to potting compost to carry on growing

Pros and Cons

You can be fairly sure you will get the characteristics because it will be genetically identical and it is possible to reproduce. If they suffer from disease they will all have the same problem

18 of 18


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all DNA and inheritance resources »