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.
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