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Energy and Activity

Feeding, Breathing and Activity

♥ Energy is needed for all the activities that living organisms carry out.

♥ An organism which is very active needs more energy than an organism which is resting.

♥ Animals and fungi get their energy by feeding upon other organisms. They are called heterotrophs.

♥ Green plants make their own food using sunlight energy. They are called autotrophs.

♥ Some foods eaten by animals contain more energy than others. Foods rich in fats or oils contain a lot of energy.

♥ Respiration releases the energy from food using oxygen.

♥ The more energy an organism needs the more oxygen it will consume.


Activity in a Changing Climate

♥ The activity of an animal often depends upon the temperature of the environment.

♥ Animals can be divided into two groups: 'warm-blooded' animals and 'cold-blooded' animals.

♥ 'Warm-blooded' animals have a constant body temperature.

♥ 'Warm-blooded' animals keep cool by sweating, panting or licking their bodies; by sending blood to the skin; by moulting their fur or feathers; by resting.

♥ 'Warm-blooded' animals stay warm by not sweating; by keeping the blood to the centre of their bodies; by covering their bodies in a thick layer of insulation; by shivering; by making heat energy in their vital organs.

♥ For a 'warm-blooded' animal to stay warm in a cold environment requires energy. Therefore, these animals must eat more food and breathe more oxygen when the weather is cold.

♥ 'Cold-blooded' animals keep their body temperature constant by changing their behaviour.

♥ When a 'cold-blooded' animal wants to warm up it can bask in the sun.

♥ When a 'cold-blooded' animal wants to cool down it hides in the shade.


How Plants Survive the Winter

♥ Many plants survive winter as seeds, as underground storage organs or with their leaves protected as buds.

♥ Seeds are produced in fruits and the fruit helps to disperse the seeds from the parent plant.

♥ Seeds in the soil may germinate immediately or they may lie dormant in the soil seed bank for many years.

♥ Dormant seeds will germinate if the soil is disturbed by fire or cultivation.

♥ The seeds need certain conditions for germination to occur. These conditions generally include warmth and water.

♥ Seeds can sense it is the right season to germinate by detecting changes in temperature or changes in the length of the day.

♥ Underground storage organs are also formed when the plant senses winter approaching. The air temperature cools and the days get shorter.

♥ Deciduous trees lose their leaves in winter. The next year's leaves are protected inside buds. The buds will only open if they sense that winter has passed and spring is approaching.

♥ Trees may help to protect themselves in winter by adding sugar to their sap. This acts as an antifreeze.


Colonizing and Populating Habitats

Seeds and Spores

♥ Plants which live on land are not very mobile. If they are going to colonize new habitats they need some way of dispersing themselves.

♥ Flowering plants and conifers disperse themselves as seeds. These contain the embryo plant with its food supply. They are surrounded by a fruit which helps them to disperse by wind, by water, by using animals or by explosion.

♥ The method of dispersal used usually depends upon where the plant is normally found growing; for example, open windy places or near water.

♥ Not all land plants use seeds to disperse themselves; other plants use spores.

♥ Spores are microscopically small so that they can be carried easily by the wind.

♥ The mosses and liverworts are small simple plants which produce spore cases on a stalk so that the spores are easily caught by the wind.

♥ The spore capsule and spores of liverworts and mosses are the result of a sperm cell fertilizing an egg cell on the parent plants.

♥ Fertilization in these plants needs water for the sperms to swim in.

♥ When the spores of these plants land in a suitable habitat, they germinate and grow into new liverworts or mosses.

♥ The fern plants also produce spores in spore cases which grow underneath their fronds.

♥ When spores of ferns germinate they do not grow into a new fern plant, they grow into a small plant called a prothallus.

♥ It is on the prothallus that fertilization takes places. The result of fertilization is a new fern plant.

♥ Fertilization on the prothallus requires water for the sperms to swim in.


When the Climate is Too Cold for Animals to Remain Active

♥ In winter, 'cold-blooded' animals may survive in a resting state such as an egg or a pupa or they may hide themselves from the cold and become torpid.

♥ 'Warm-blooded' animals survive winter by remaining active if there is enough food and shelter, by migrating to a warmer climate or by hibernating to save energy.

♥ Hibernating mammals and birds have a low body temperature, a slower heart beat and a slower breathing rate.

♥ Hibernating mammals and birds can control their body temperature. If their temperatures fall towards freezing point they can warm themselves up. 'Cold-blooded' animals cannot do this.


Animal Life Cycles and Dispersal

♥ Insects and other invertebrates go through a life cycle where their bodies change dramatically in shape as well as size. This is called metamorphosis.

♥ The immature stages of insects are called larvae or nymphs. They feed and grow rapidly.

♥ The adult stages are mature; they can reproduce. They usually have wings so that they can disperse their eggs over a large area.

♥ The insect body is covered by an exoskeleton which is hard and will not permit the insect to grow bigger. The larva or nymph has to periodically moult its exoskeleton and a grow a new one which is bigger.

♥ The immature insects develop into adults in two ways: by complete metamorphosis or by incomplete metamorphosis.

♥ Insects which show complete metamorphosis have immature stages called larvae. The larva passes through a resting stage called a pupa to change into an adult.

♥ Insects which show incomplete metamorphosis have immature stages called nymphs. The nymphs look like small adults without wings. As the nymphs grow they come to look more and more like the adult stage. In these insects there is no pupa.


Asexual Reproduction

♥ Sexual reproduction requires sex cells (sperms and eggs produced by males and females) but asexual reproduction requires no sex cells at all.

♥ Asexual reproduction is common amongst plants, single-celled organisms and simple animals.

♥ Asexual reproduction has the advantage of producing large numbers of offspring very quickly.

♥ A group of offspring produced by asexual reproduction from a single parent is called a clone.

♥ Asexual reproduction in a single-celled organism involves simply dividing into two or the budding of a small piece of the mother cell.

♥ Simple animals, such as the Hydra, may also bud off small pieces which have grown from their bodies.

♥ Green plants are quite sophisticated in their methods of asexual reproduction. Offspring may be produced by runners, bulbs, rhizomes or tubers.

♥ Gardeners have used this ability of plants to reproduce asexually. They take cuttings from plants and encourage them to grow roots and leaves. In this way large numbers of the same plant can be obtained very quickly from one parent plant.

♥ Scientists have gone one step further; they cultivate very small pieces of plants in test tubes. This is called in vitro culture and it can produce thousands of identical offspring from one plant, all grown under carefully controlled conditions.


Sexual or Asexual Reproduction?

♥ Asexual reproduction is quite rapid and requires only one parent.

♥ The offspring produced by asexual reproduction, from the same parent, are all identical to one another and they are identical to the parent.

♥ Sexual reproduction requires sex cells produced by two parents (a male and a female). Sexual reproduction is more complex and slower than asexual reproduction.

♥ Offspring produced by sexual reproduction look like their parents but they are not identical (unless they are identical twins); they show variation.

♥ Farmers breed together different varieties of animals or plants to produce offspring which show the best characteristics of both parents.

♥ Amongst populations of wild animals and plants, species show variation as a result of sexual reproduction. This variation allows them to adapt to new environments.

♥ If a species of organism which shows no variation cannot adapt it may become extinct.


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