National 5 NAR revision

1. National 5 NAR revision Multicellular organisms

2. Cells tissues and organs There are many different specialised cells in animals and plants. They include; Sperm cells have a tail to allow them to swim towards the egg. Red blood cells have a biconcave shape to give a large surface area to absorb oxygen Phloem have sieve plates to allow sugar to move from one cell to the next They also have haemoglobin to carry oxygen around the body

3. Stem cells Stem cells are at the centre of many research projects at the moment. They can be used to • Grow replacement organs such as an oesophagus, • Repair damaged heart tissue • Grow new skin cells for a skin graft The use of embryonic stem cells is controversial as they mean destroying an embryo. At the moment, they are the only stem cells which can become any type of tissue.

4. Meristems Plants are able to grow continuously from select points. These regions of undifferentiated cells are called Meristems. They are found at root and shoot tips. meristem

5. Control and communication The brain and central nervous system has many different parts. Cerebrum – conscious thought, memory and reasoning Medulla – breathing and heart rate Cerebellum – balance and muscular co-ordination

6. Reflexes If you touch something sharp your limb will withdraw before you know it. This is called a reflex arc. By relay neuron

7. Flower structure Brightly coloured and scented to attract insects Produces male gamete - pollen Produces female gamete - ovule Female gamete Remember, when the haploid pollen grain fertilises the haploid ovule, a diploid zygote is formed.

8. Inheritance We receive all our genetic information from our parents. In genetics, there are some terms to learn. genotype The set of genes possessed by an organism phenotype The physical appearance of the organism heterozygous Possessing two different forms of the gene homozygous Possessing two identical forms of the gene dominant Characteristic which is always expressed recessive Characteristic which is masked by the dominant one

9. Need for transport Plants need water from the soil to carry out photosynthesis. They absorb it through the roots and transport it to the leaves through xylem tissue. The xylem has rings of lignin to keep the vessel open and strengthen the plant

10. Stomata and transpiration The leaves lose water constantly through the stomatal pores. This is called TRANSPIRATION Transpiration is affected by the following factors: Wind speed Temperature Humidity Light intensity

11. Stomata The function of the stomata is to allow CO2 to enter the leaf for photosynthesis and let O2 to leave. For this reason, the only need to be open during the day. The guard cells swell to open and shrink to close.

12. Blood vessels Arteries have a thick, elastic muscular wall to withstand the high pressure of the blood travelling away from the heart. Elastic Wall Ring of Muscle Blood

13. Veins Veins are under less pressure and have much thinner walls. To keep blood moving back to the heart, they need valves to prevent backflow of blood. Thin Inelastic Wall Blood Valve

14. Capillaries Capillaries are where materials are exchanged between the blood and tissues. They are only one cell thick to allow diffusion to happen quickly and easily. Very thin wall Blood

15. Effect of lifestyle Heart disease is a Western problem. There are a number of lifestyle choices which can increase your risk of developing it. • High-fat or high-salt diets • Smoking • Drinking • Lack of exercise • High-stress environment Reducing or stopping these can help reduce your chances of developing heart disease.