National 4 Unit 2
Multicellular Organisms
Revision Notes
Key Area 1 – Sexual and asexual reproduction and their importance for survival of species
All organisms reproduce to ensure survival of the species and to prevent the species becoming extinct.
Fertilisation occurs when the nucleus of the sperm cell and the nucleus of the egg cell fuse.
Sexual reproduction:
- In plants:
- Pollen grains are transferred from the anther of one plant to the stigma of another plant.
- Some plants are pollinated by insects (like bees) and birds but other plants are pollinated by the wind.
- In animals:
- Internal Fertilisation – when fertilisation happens insidethe female’s body.
- External Fertilisation – when fertilisation happens outsidethe female’s body.
Asexual Reproduction:
New plants are produced from a single parent without involving sex cells. New plants that are genetically identical to one another and to their parent plant are called a clone.
Types of asexual reproduction in plants
•Bulbs – plant produces leaf bases, swollen with stored food, e.g. daffodils.
•Runners– plant produces side shoots e.g. spider plant, strawberries.
•Tubers– plant produces underground storage organs e.g. potatoes.
Advantages for sexual reproduction:
•Variation in offspring
•Organisms are well distributed so more chance of survival and less competition
Advantages for asexual reproduction (in plants):
•Young plant has its own food store
•Pollination plays no part
•Young plant produced in environment that suits growth of parent plant
Key Area 2 – Propagating and growing plants
Seed Structure: The embryo becomes the adult plant; the food store, stores food and the seed coat protects the seed.
Conditions for germination:
Suitable temperature
Oxygen
Water
Artificial propagation means increasing the supply of a type of plant using some method of that the plant itself would be unable to carry out.
Cuttings are the simplest way to artificially propagate a plant. A branch from the parent plant is cut off, its lower leaves are removed and the stem is planted in damp compost.
Layering is a method of propagation by which a shoot is made to rootwhile still attached to the parent plant.
Key Area 3 – Commercial use of plants
Commercial uses of plants
Oil seed rape is used to make oils and lubricants.
Large brown seed weeds are used to make toothpaste, jelly, ice cream and wallpaper paste.
Poppies and Foxgloves are used in medicine.
Plants are protected from wind, rain, frost and pests in greenhouses. This means crops will grow faster and more crops will be produced.
Key Area 4 – Genetic information
The appearance of an organism is itsphenotype – the physical appearance resulting from the inherited information. The genotype is the genetic make-up of an individual. Each parent gives their offspring one gene for each characteristic.
The genotype determines the organism's phenotype.
Here is a worked example:
Brown hair is dominant to red hair (it is called recessive) and we can tell this because none of the children had red hair. We can prove this by looking at the parents genes and completing a punnet square.
All the children have brown hair but carry the red haired gene. This means next generation could have red hair (this is where the phrase ‘skip a generation’ comes from). You only need 1 dominant gene for it to show.
Key Area 5 – Growth and development of different organisms
A balanced diet, suitable conditions, water, minerals and vitamins are required for healthy growth and development.
Cress seeds
Seeds need certain conditions to germinate:
Suitable temperature
Oxygen
Water
Without these conditions they will not germinated. Remember seeds don’t need light to germinate (most seeds are underground!).
Humans
Cigarette smoke contains:
•Tar – causes lung cancer.
•Nicotine – is an addictive drug and affects how your brain works.
•Carbon monoxide– is a poisonous gas which stops the blood carrying oxygen.
Therefore smoking can lead to asthma, poor circulation (especially to the legs and feet), angina (chest pains), heart attacks, stroke, high blood pressure, heart disease and lung and throat cancer.
Key Area 6 – Biological actions in response to internal and external changes to maintain stable body conditions.
Homeostasis is the maintenance of the body’s internal environment despite changes to the external environment.
Body Temperature
If you get too cold:
You shiver, so your muscles produce heat.
Blood goes away from the skin and your hands and feet to the core of the body - so you gopale and your hands don’t work as well.
If you get too hot:
You sweat, and your body cools down when it evaporates.
Blood goes to the skin away from the core of the body, so you look red and lose more heat from your skin.
Blood Glucose
When we eat we provide a supply of sugar and if there is any extra then we can store it in our body.
Insulin
GlucoseGlycogen
Glucagon
GlycogenGlucose
Insulin and glucagon are released from the pancreas and glycogen is stored in the liver.
Diabetes
If the blood sugar level cannot be controlled a person would suffer from diabetes. Type 1 diabetes usually appears early in a person’s life whereas type 2 usually appears later in life.
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