1. Paper 1 revision
What people forget?

2. What students forget

3. Circular pieces of DNA
Often contain genes that help with the survival or the organism such as antibiotic resistance

4. Algae
Photosynthetic organisms

5. The sheath acts as an insulator - rather like the plastic coating of an electrical wire. Neurones are adapted to their function by being long, so that they communicate with distant parts of the body. They also have branched endings called dendrites. These connect with many other neurones.

6. Before a cell can divide it needs to grow and increase the number of sub-cellular structures such as ribosomes and mitochondria.
The DNA replicates to form two copies of each chromosome.
In mitosis one set of chromosomes is pulled to each end of the cell and the nucleus divides.
Finally the cytoplasm and cell membranes divide to form two identical cells

7. A meristem is the tissue in most plants containing undifferentiated cells, found in zones of the plant where growth can take place (tips of roots and shoots)

8. Therapeutic cloning
If you were to receive medical treatment with cells grown from stem cells, your body’s immune system would recognise the cells as foreign, and they would be rejected and die. But this would not happen if you received cells with the same genes as you.
This could be done by cloning one of your cells to produce an embryo, then taking stem cells from this. This is called therapeutic cloning. Here are the steps involved:
nucleus taken out of a human egg cell
nucleus from a patient's cell put into the egg cell
egg cell stimulated to develop into an embryo
stem cells taken from the embryo
stem cells grown in a container of warm nutrients
stem cells treated to develop into required cell types

9. Unicellular organisms have a large surface area compared to their volume with makes diffusion easy and supplies their needs
However large multi-cellular organisms have a small surface are to volume ratio and therefore have had to develop transport and exchange systems to supply their needs.

11. Natural pacemaker cells are found in the right atrium
They control the natural rhythm of the heart
If that goes wrong an artificial one can be used.

12. The valves in the heart stop the blood flowing backwards
The valves in the heart stop the blood flowing backwards. If the valves are damaged or weak, they cannot stop this backflow so well. The blood circulation is reduced, again leading to tiredness and shortness of breath. The faulty valves can be replaced by artificial valves.

13. Risk factors
Substances in a persons body or environment that increases the risk of disease.

14. liver cirrhosis – excessive alcohol consumption
lung cancer – smoking
premature babies – drinking alcohol and smoking whilst pregnant
skin cancer – exposure to UV radiation

15. benign tumours grow slowly and are usually harmless – warts are benign tumours
malignant tumours often grow more quickly and may spread throughout the body.

16. Translocation is the movement of materials from leaves to other tissues throughout the plant.

17. Bacteria release toxins
Viruses damage cells

18. indirect protection from infectious disease that occurs when a large percentage of a population has become immune to an infection, thereby providing a measure of protection for individuals who are not immune

19. Traditionally drugs were extracted from plants and microorganisms.
• The heart drug digitalis originates from foxgloves.
• The painkiller aspirin originates from willow.
• Penicillin was discovered by Alexander Fleming from the Penicillium mould.

20. Photosynthesis is endothermic as it take in energy
Respiration is exothermic as it gives out energy

22. Anaerobic respiration in plants and yeast
Glucose  ethanol + carbon dioxide In yeast it can also be called fermentation and it used for brewing and baking

23. Metabolism is the sum of all the reactions in a cell or the body
The energy transferred by respiration in cells is used by the organism for the continual enzyme controlled processes of metabolism that synthesise new molecules.
Metabolism includes:
• conversion of glucose to starch, glycogen and cellulose
• the formation of lipid molecules from a molecule of glycerol and three molecules of fatty acids
• the use of glucose and nitrate ions to form amino acids which in turn are used to synthesise proteins
• respiration
• breakdown of excess proteins to form urea for excretion.