National 5 NAR revision

Multicellular organisms

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

They also have haemoglobin to carry oxygen around the body

Phloem have sieve plates to allow sugar to move from one cell to the next

Stem cellsStem 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.

Meristems

Plants are able to grow continuously from select points.

These regions of undifferentiated cells are calledMeristems.They are found at root and shoot tips.

meristem

Control and communicationThe brain and central nervous system has many

different parts.Cerebrum – conscious thought, memory and reasoning

Cerebellum – balance and muscular co-ordination

Medulla – breathing and heart rate

Reflexes If you touch something sharp your limb will

withdraw before you know it. This is called a reflex arc.

By relay neuron

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.

InheritanceWe 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

Need for transportPlants 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

Stomata and transpiration

The leaves lose water constantly through the stomatal pores. This is called

TRANSPIRATION

Transpiration is affected by the following factors:Wind speedTemperatureHumidityLight intensity

StomataThe 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.

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

VeinsVeins 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

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

Effect of lifestyleHeart 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.