1. Multicellular organisms
National 5 NAR revision
Multicellular organisms

2. Producing new cells

3. Stages Chromosomes are replicating
Chromosomes shorten and thicken so they are now visible
Chromosomes line up at the equator and spindle fibres attach at the centromere
Chromatids are pulled apart to opposite sides of the cells
Nucleus reforms in each new daughter cell and cytoplasm divides

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

5. 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.

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

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

8. 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.

9. 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

10. 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

11. 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

12. 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.

13. 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

14. 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

15. 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

16. Absorption of materials
The alveolus in the lungs has a number of features that make it efficient at gas exchange.
Large surface area
Thin lining
Moist
Good blood supply