Biology B3

Animal Cell Structure
a) nucleus - contains DNA
b) cell membrane - holds cell together
c) Ribsome - where proteins are sythensised
d) cytoplasm - gel-like substance where chemical reactions happen
e) mitochondria - where most of the reactions in respiration take place.

Plant Cell Structure
a) nucleus
b) cytoplasm
c) chloroplasts
d) cell wall - made of cellulose supports the cell
e) vacuole - a relatively large structure that contains cell sap(solutuon of sugar and salts)
d) cell membrane

Bacteria cells are smaller and don't have chloroplats, mitochondria and a true nucleus.

Chromosomes
1) Chromosomes are long olecules of coiled up DNA
2) DNA is a double helix containing 4 different bases
3) A, C, G and T
4) Each base froms cross links to a base on the other strand
5) A - T , C - G, called complementary base-pairing

Watson and Crick
1) Francis Crick and James Watson were the first scienstists to build a model of DNA - 1953
2) They used x-ray data showing DNA is a double helix and other research showing pairs of bases

DNA Can Replicate Itself

1) DNA copies itself every time a cell divides, so that each new cell still has the full amount of DNA.
2) The DNA double helix first 'unzips' forming two single strands, free nucleotides join on forming an exact copy.

Proteins1) DNA controls the production of proteins in a cell
2) A section of DNA that codes for a particular protein is called a gene
3) Proteins are made up of chains of molecules called amino acids.
4) The amino acids are joined together to make proteins, following the order of the bases in the gene.
5) Each gene contains a different sequence of bases - which is what allows it to code for a unique protein.

mRNA Carries the code to the Ribosomes

1) Proteins are made in the cell cytoplasm by tiny structures called ribosomes.
2) To make proteins, ribosomes use the code in the DNA. The cell needs to get the code from the DNA to the Ribosome.
3) This is done using a molecule called mRNA, whichis made by copying the code from DNA.
4) The mRNA acts as a messanger between the DNA and the ribosome.

4 Proteins to remember:
a) Enzymes
b) Carrier Molecules - used to transport smaller molecules, e.g haemoglobin
c) Hormones - used to carry messages around the body
d) Structural Proteins - are physically strong
Enzymes
1) Living things produce enzymes, which act as biological catalysts.
2) Every different biological reaction has its own enzyme designed especially for it.
3) Each enzyme is coded for by a different gene and has a unique shape which it needs to do its job.

Matching Enzymes
1) Each enzyme has an active site - where it joins to its substrate
2) Enzymes are really picky, they usually only work with one substrate.
3) This is called the 'lock and key' mechanism

A mutation is a change in the DNA base sequence. If a mutation occurs within a gene, it could stop the production of the protein the gene normally codes for or produce a different protein.

Most Mutations are Harmful1) Producing the wrong protein or no protein at all can be a bit of a disaster, especially if the protein is an important enzyme.
2) If a mutation occurs in reproductive cells, then the offspring might develop abnormally or die at an early stage of their development.
3) If a mutation occurs in body cells, the mutant cells can sometimes start to multiply in an uncontrolled way and invade other parts of the body.

Some Mutations are Beneficial, Some have No Effect
1) Natural selection allows a different protein which is an improvement to be passed on giving the offspring produced a survival advantage. Eventually, the mutation becomes common.
2) Some mutations also have no effect, they don't change the protein being coded for.

Advantages of being Multicellular
1) Can be bigger, travel further and get your nutrients from various sources, being bigger also means fewer things can eat or squash you.
2) Allows for cell differentiation, meaning different types of cells can do different jobs.  A cell can be adapted for a certain job.
3) Means multicellular organisms can be more complex, they can have specialised organs.

Mitosis
Mitosis is when a cel reporduces itself by splitting to form two idetical offspring.
This happens in the body when you want identical cells, Mitosis diagram below:

Meiosis + GametesGametes are formed by meiosis in the ovaries and testes. Gametes are the sex cells - eggs and sperm.

Meiosis Involves Two Divisions1) finishes with 4 cells
2) in the first division the pair of chromosomes split, each containing one of each of the 23 types of chromosomes.
3) The second division of meiosis is like mitosis, each chromosome splits in half and one arm ends up in each new cell.

Fertilisation creates Genertic Variation
1) At fertilisation male and female gametes combine to form a diploid cell. This cell is called a zygote. The zygote is controlled by the combination of genes of genes allowing for genetic variation.
Sperm Cells are adapted for their function as they are small and have long tails so they can swim to the egg. The also have lots of mitochondria to provide the energy neede to swim the distance.

Growth
-Animals stop growing, plants an grow continuosly
-In animals, growth happens by cell division. In plants, growth in height is mainly due to cell enlargement.

Stem Cells
1) Differentiation is the process in which a cell changed to become specialises for its job. PLant cells never lose this ability.
2) Most cells in your body are specialised for a particular job
3) Embryos have the potential to turn into any kind of cell

Stem Cells could be a cure to many disorders
1) medicine already uses stem cells to cure disease. People with blood disorders can be cured by bone marrow transplants.
2) Some people are against stem cell research as the believe every embyros should have the potential to be a human life.

3 Methods of Measuring Growth
1) Length - simply measuring the length of a plant or animal, easy to measure but it doesn't tell you about changes in width, diameter, number of branchges etc.
2) Wet mass - weigh the plant or animal, this is the wet mass, easy to measure but wet mass is very changeable, e.g a plant will be heavier if its rained.
3) Dry mass - dry out the organism before weighing it, not affected by the amount of water in a plant or how much an animal has ate, you might have to kill the organism to work it out.

Phases of Human Growtha) infancy - first two years of life, rapid growth
b) childhood - period between infancy and puberty, steady growth
c) adolescence - begins with puberty, rapid growth
d) maturity/adulthood - preiod between adolescence and old age. Growth stops
e) Old age - usually considered to be between age 65 and death.
- organisms don't grow evenly. Different parts of the body will grow at different rates.

Respiration  occurs in every cell in the body and is the process of releasing energy from glucose. The energy from respiration can't be used directly by cells so it is used to make a substance called ATP.
Respiration is controlled by enzymes meaning it is affected by both temp and pH.

Aerobic Respiration
This happens when there's plenty of oxygen available, this is the most efficeient way to release energy from glucose. This is the most common respiration
Formula: glucose + oxygen -> carbon dioxide + water (+energy)

Anaerobic Respiration uses no oxygen
This is used when your body can't supply enough oxygen to your muscles, this is not the best way to convert glucose to energy because it releases less energy per glucose molecule. In anaerobic respiration glucose is only partly broken down and lactic acid is produced.
Formula: glucose -> lactic acid (+energy)
Afterwards you will need extra oxygen to break down the lactic acid

Plasma is a pale yellow liquid which carries:
1) Red blood cells, white blood cells, platelets
2) Water
3) Digested food products like glucose and amino acids from the gut to all the body cells
4) Carbon Dioxide from the body cells to the lungs
5) Urea from the liver to the kidneys
6) Hormones
7) Antibodies

Red blood cells have the job of carrying oxygen
They are adapted to this by:
a) small and biconcave shape to give large surface area to volume ratio to absorb oxygen.
b) contain haemoglobin, contains a lot of iron
c) don't have a nucleus freeing up space
d) very flexible

3 Different Types of blood vessels:
1) Arteries - these carry blood away from the heart
2) Capillaries - these are involved in the exchange of materials at the tissues
3) Veins - these carry blood to the heart

Arteries1) The heart pumps blood out at high pressure so the artery walls are strong and elastic

Capillaries
1) Arteries branch into capillaries, these are tiny and only one cell thick

Veins
1) capillaries join up to form veins, the blood is at lower pressure in the veins so the walls don't need to be as thick, they also halve valves to help keep the blood flowing in the right direction

Double Circulatory System
1) The first system connects the heart to the lungs, the deoxygenated blood is pumped to the lungs to take in oxygen, this then reutns to the hearth.
2) The second system connects the heart to the rest of the body. The oxygenated blood in the heart is pumped out to the body.
The Advantage of this is that it increases the rate of blood flow to the tissues.

Selective breeding is when humans artificially select the plants or animals that are going to breed and have their genes remain in the population.
Organisms are selectively bred to develop the best features, examples:-maximum yield of meat, milk, grain, etc
-good health and disease resistance

Process
a) From your existing stock select the ones which have the best characteristics
b) Breed them with each other
c) Select the best of the offspring, and breed them together
d) Continue this process over several generations, and the desirable trait gets stronger and stronger

The main disadvantage of selective breeding is a reduction in the gene pool!

Genetic Engineering is the moving of genes from one organism to another so that it produces useful biological products.
Advantage - you can produce organisms with new and useful features very qucikly.
Disadvantage - main risk is that the inserted gene might have unexpected harmful effects.

Stages
1) First the gene that's responsible for producing the desirable characteristic is selected
2) It's then 'cut' from the DNA using enzymes, and isolated.
3) The useful gene is insterted into the DNA of another organism
4) The organism then replicates and soon there are loads of similar organisms all producing the same thing

3 Examplessome populations rely heavily on rice for food, they form vitamin A deficiency, they then change the gene in rice plants to compesate the deficiency.
Plants that are resistance to disease can be engineered so that more crops can be resistant
There are moral and ethical issues involved, people worry it will get to far and we will start to choose how we want our children.

Curing Genetic DisordersGene therapy involves altering a person's genes in an attempt to cure gentic disrders. Scientists haven't got it to work properly yet, but they're working on it for the future.
Two Types of gene therapy:
- The first would involve changing the genes in body cells, particularly the cells that are most affected by the disorder.
-The second type of gene thera[py would involve changing the genes in the gametes. This means that every cell of an offsrping produced from these gametes will be affected by the gene therapy.

Cloning is making an exact copy of another organism. Clones are genetically identical organisms.

Benefits of Cloning
1) Cloning allows you to mass produce animals with desirable characteristics
2) Human embryos could be produced by cloning adult body cells 
Risks
1) There is some evidence that cloned animals might not be as healthy as normal ones
2) Cloning is a new science and it might have consuquences that we're not yet aware of.

Cloning Humans is a possibility - with a lot of Ethical Issues

a) Clones of other mammals have been unhalthy and often die prematurely meaning humans could too
b) even if a healthy clone were produced, it might be psychologically damaged by the kowledge that it's just a clone of another human being.

How to Clone Plants
1) Gardeners take cuttings from good parent plants and then planting them to produce genetically identical copies, clones, of the parent plant.
2) Cloning plants is easier than cloning plant cells because plant cells keep the ability to differentiate.