[4 marks Questions]

Question 14 Marks

Explain evolution from wild cabbage using the artificial selection.

Answer

Varied organisms are evolved from common ancestor.
From wild variety of cabbage several different varieties of plants are cultivated by artificial selection.
Before two thousand years farmers were producing wild cabbage as an edible variety of plant.
It’s closely arranged leaves at short distances were used as food.
Some farmers have obtained variety of cabbage in which flower development was arrested and then they were cultivated as broccoli.
Some farmers have obtained variety of cabbage having sterile flowers and they were cultivated as cauliflower
Some farmers selected the swollen portion of the wild cabbage and developed new variety called Kohlrabi from this.
Some farmers have developed a few larger leaves of the wild cabbage as a new variety called Kale, a leafy vegetable.
All these varieties are apparently quite different individually from the ancestral wild cabbage.

Question 24 Marks

Describe the sex determination in human beings.

Answer

The sex determination in human beings is due to chromosomes and thus it is genetically determined.
Human beings have $23$ pairs of chromosomes.
Each pair has one maternal and one paternal copy.
$22$ pairs of chromosomes are similar in both male and female.
They are called autosomes, as they decide body characters.
$23$rd pair has sex chromosomes.
Women have a pair of $X$ chromosomes, i.e., females are therefore $XX$.
Men have a mismatched pair in which one is normal sized $X$ while the other is a short one called $Y$, i.e., Males are therefore $XY$.
As shown in figure, the probability of getting a male (boy) or a female (girl) child is $50 \%$.
All children will inherit an X-chromosome from their mother regardless of whether they are boys or girls.
Thus, the sex of the children will be determined by what they inherit from their father.
A child who inherits an X-chromosome from father will be girl and one who inherits a Y-chromosome from father will be a boy.

Question 34 Marks

What is sex determination? State the different methods of sex determination in animals.

Answer

The unisexual organism is either a male or a female.
The mechanism by which the sex of an individual is determined is called sex determination.
The organism that develops from the fertilised egg (zygote) may be a male or a female offspring.
Methods of sex determination in animals:
Different species of animals utilize different methods for their sex determination.
e.g., $(1)$ In a few reptiles, the sex determination is dependent on the environmental factor, i.e., temperature.
The egg (zygote) may develop into a male turtle or a female turtle, is determined by temperature.
When a temperature is over $30 °C$, the eggs of turtle, develop into female.
The eggs of crocodiles exposed to the high temperature induce the development of male whereas the lower temperature induces the development of female crocodiles.
$(2)$ In human beings the sex of the individual is determined by sex chromosomes and is thus genetically determined.
The genes inherited from parents decide the sex of the offspring.
Exception:
The animal such as certain snail can change its sex.
The sex therein, is not genetically determined.

Question 44 Marks

Explain creation of diversity over succeeding generation.

Answer

Variations do appear during reproduction whether organisms multiply asexually or sexually.
Heredity involves inheritance of basic body design, as well as subtle changes in it from one generation to the next generation.
The second generation will have differences that they inherit from the first generation, as well as newly developed differences.
As shown in diagram, the original organism at the top will give rise two individuals/ bacteria through asexual reproduction.
Both similar in body design, but with subtle differences.
Resultant two individuals/ bacteria divide again, each of them, in turn, will give rise two individuals in the next generation.
Each of four individuals will be different from each other.
In this way, large number of individuals are formed after many generations.
While some of these differences will be unique, others will be inherited from their respective parents, who were different from each other.
The differences between them, are generated due to small inaccuracies in $DNA$ copying.
Thus, variation is accumulated in each generation during reproduction which gives rise to diversity.

Science [4 marks Questions]