Evolution — BIOLOGY STD 12 Science — Question

Differentiate between microsporogenesis and megasporogenesis. Which type of cell division occurs during these events? Name the structures formed at the end of these two events.

1. Write the scientific names (binomials) of the causative organisms of pneumonia.
2. How does a healthy person acquire infection of this disease?
3. Mention the characteristic symptoms of the disease.

Describe the disease 'Typhoid' under the following headings :
(i) Name of the pathogen
(ii) Name of the test to confirm the disease
(iii) Mode of infection
(iv) Four main symptoms of the disease
(v) Diagram of the structure of an antibody molecule.

Explain the mechanism of evolution.

State the modifications of forelimb in animals as an example of homology.

In a biology class, teacher was telling the students that the structures/components and their functions in a watch can be compared with various levels of organisation we find in nature. Radhika was surprised and asked teacher to explain it. Teacher got impressed with Radhika's interest and explained that there is a systematic arrangement of smaller and simpler components into larger one in a hierarchy or pyramid having different levels where each level is formed of components of lower level and itself becomes part of higher level for achieving a common goal.
(i) What are the four levels of biological organisation found in nature?
(ii) What is the basic unit of ecological organisation?
(iii) Define community.
(iv) What values are shown by Radhika?

With the help of a diagram explain the structure of DNA.

Starting with the zygote, draw the diagrams of the different stages of embryo development in a dicot.

Rose plants produce large, attractive bisexual flowers but they seldom produce fruits. On the other hand a tomato plant produces plenty of fruits though they have small flowers. Analyse the reasons for failure of fruit formation in rose.
Both these plants - rose and tomato - both selected by human beings for different characteristics, the rose for its flower and tomato for its fruit. Roses, being vegetatively propagated do not need to produce seeds.

The density of a population in a habitat per unit area is measured in different units. Write the unit of measurement against the following:

a.	Bacteria	____________
b.	Banyan	____________
c.	Deer	____________
d.	Fish	____________