E xamples of Intermediate link

Lung fish

(link between fish and amphibians)

Archaeopteryx

(link between reptiles and birds.

Give Reasons:

1. The fossil of archaeopteryx is an evidence for evolution. because the archaeopteryx shares features with reptiles such as the jaws, sharp teeth, a long bony tail and claws on its wingtips. Also it has features like birds such as the feathery wings for flying.

2. Lung fish is considered as link between fish & amphibians. This fish breathes through its gills like all fish however it also has lungs like amphibians to use it in breathing in case of low oxygen water environment such as swamps.

3. The Black Biston betularia butterflies spread with the industrial evolution. Natural selection allowed these type of butterflies to survive because they're not easily spotted by predators when they rest on tree trunks blackened by soot.

Give Reasons for:

The appendix is considered vestigial organ in humans. In herbivores (plant eaters), the appendix helps digest the cellulose in plants . It's believed that humans had ancestors who fed on plants & the appendix helped in digestion , with evolution humans nowadays , don't have a function for the appendix(the appendix is still present but very small).The human retains evidence of structures that are probably relics from previous mammalian ancestors. This feature has little apparent function in modern humans. Relic features such as the appendix are called vestigial organs. The appendix is a narrow tube attached to the large intestine. In some plant-eating mammals, the appendix is a functioning organ that helps to digest plant cellulose. In humans, however, the organ lacks this purpose and is reduced in size. Herbivores have large appendices while carnivores lack them.

a. At their early stage, the embryos of many animals look similar.

b. Embryos of many vertebrates have gills first.

c. These gills disappear later.

d . The heart starts with one auricle and one ventricle then develop into 4 chambers.

A ll the limbs of vertebrates have five digits. These limbs are modified to suit movement in their environment

• W

  The limbs of some vertebrates

  ings for flying

• Hooves for running

• Peddles for swimming

• H oofed animals have only one digit .

Class	Nitrogenous wastes	Figures	Reasons
Fish & Tadpole	Ammonia		Ammonia is soluble in water and passes out through the gills.
Reptiles & Birds	Uric acid		Uric acid is insoluble in water , it is excreted with small amount of water.
Amphibians & Mammals	Urea		Urea is soluble in water , it is excreted with large amounts of water in the urine.

The Modern Synthetic theory corrects the defects in Darwin's theory .

Biological equilibrium

The tendency of the environment to restore its normal level after being disturbed.

e.g. An animal preys on another till the prey almost perishes in the environment. The predator switches to another prey & over time the first prey reproduces enough to restore its population.

Hardy & Weinberg's law:

The rate of gene distribution tends to be constant in a population therefore the characteristics in the population are constant.

The conditions that keep the genetic equilibrium of the population are:

1. The population must be large.

2. Mating is random.

3. Natural selection is absent.

4. The individuals don't migrate into the population or out of it.

5. Mutations are absent.

If these conditions are absent , the characteristics of the individuals vary , this is called genetic drift which causes the evolution of the population.

Give Reasons :

1. Variation among the individuals of a species. Mating between organisms of different genotypes produces new phenotypes . 2. Variation in population causes evolution. The variation allows the organisms to survive in a changing environment. Reasons for variation among individuals of species.

3.Mating between organisms of different genotypes → new phenotypes (characteristics) appear.

4.Environmental factors → gene mutation.

5.Crossing over during meiosis.