Short Answer TypeWhy are angiosperm anthers called dithecous? Describe the structure of its microsporangium
A typical angiosperm anther is bilobed with each lobe having two theca, thus they are called dithecous.
Microsporangium is nearly circular in outline. It is surrounded by four wall layers that is the epidermis, endothecium, middle layers and the tapetum. The outer three wall layers perform the function of protection and help in dehiscence of anther to release the pollen. The innermost wall layer is the tapetum which nourishes the developing pollen grains. Cells of the tapetum possess dense cytoplasm and generally have more than one nucleus. When the anther is young, a group of compactly arranged homogenous cells called the sporogenous tissue occupies the centre of each microsporangium.
If implementation of better techniques and new strategies are required to provide more efficient care and assistance to people, then why is there a statutory ban on amniocentesis? Write the use of this technique and give reason to justify.
Why is pedigree analysis done in the study of human genetics? State the conclusions that can be drawn from it.
Identify ‘a’, ‘b’, ‘c’, ‘d’, ‘e’ and ‘f’ in the table given below :
|
No. |
Syndrome |
Cause |
Characteristic of affected individuals |
Sex Male/Female/ both |
|
1 |
Down’s |
Trisomy of 21 chromosome |
‘a’ (i) (ii) |
‘b’ |
|
2 |
‘c’ |
XXY |
Overall masculine development |
‘d’ |
|
3 |
Turner |
45 with XO |
‘e’ (i) (ii) |
‘f’ |
Community Service department of your school plan a visit to a slum area near the school with an objective to educate the slum dwellers with respect to health and hygiene.
(a)Why is there a need to organize such visits?
(b)Write the steps you will highlight, as a member of this department, in your interaction with them to enable them to lead a healthy life.The following graph shows the species – area relationship. Answer the following questions as directed
(a) Name the naturalist who studied the kind of relationship shown in the graph. Write the observations made by him.
(b) Write the situations as discovered by the ecologists when the value of ‘Z’ (slope of the line) lies between (i) 0.1 and 0.2 (ii) 0.6 and 1.2 What does ‘Z’ stand for ?
(c) When would the slope of the line ‘b’ become steeper ?
Name and describe the technique that helps in separating the DNA fragments formed by the use of restriction endonuclease.
State the function of a reservoir in a nutrient cycle. Explain the simplified model of carbon cycle in nature.
Since the origin of life on the earth, there were five episodes of mass extinction of species.
(i)How is the 'Sixth Extinction', presently in progress, different from the previous episodes?
(ii)Who is mainly responsible for the 'Sixth Extinction''?
(iii)List any four points that can help to overcome this disaster.
Long Answer Type(a) Where does fertilization occur in human ? Explain the events that occur during this process.
(b) A couple where both husband and wife are producing functional gametes, but the wife is still unable to conceive, is seeking medical aid. Describe any one method that you can suggest to this couple to become happy parents.
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