BIOLOGY 3 Marks Question

Structure of brain. The human brain is well protected by the skull. Inside the skull, the brain is covered by cranial meanings consisting of an outer layer called dura mater, a very thin middle layer called archnoid and an inner layer (which is in contact with the brain tissue) called pia mater. The brain can be divided into three major parts.
(i) Forebrain (ii) Midbrain and (iii) Hindbrain

i. Blood: It is specialised kind of living fluid connective tissue of opaque red colour of alkaline reaction and salty in taste. Its specific gravity is 1.050-1.060. The blood contains a fluid part of the plasma, and the solid part the corpuscles.
ii. Serum: is the name given to blood plasma which has its protein fibrinogen removed. In this form, the plasma cannot clot, so it can be stored in hospital blood banks for transfusions in emergencies.

Mitral Valve: It is situated at the atrioventricular septa. It consists of two flaps which allow the blood to flow from the left atrium to left ventricle but prevents blood flowing from flowing in the reverse direction.
Semilunar Valve: It guards the openings of the aorta in the left ventricle. Each semilunar valve is formed of semilunar cusps which pump blood to the aorta on the contraction of ventricle but prevents the backflow of blood.

Pectoral and Pelvic Girdle. Pectoral girdle is situated in the pectoral region of the body. Each half of pectoral girdle consists of a clavicle and a scapula. Scapula is a large triangular flat bone situated in the dorsal part of the thorax between the second and the seventh ribs. The dorsal, flat, triangular body of scapula has a slightly elevated ridge called the spine which projects as a flat, expanded process called the acromion. The clavicle articulates with this. Below the acromion is a depression called the glenoid cavity which articulates with the head of the humorous to form the shoulder joint. Each clavicle is a long slender bone with two curvatures. This bone is commonly called the collar bone. Pelvic girdle is situated in the pelvic region of the body.
Pelvic girdle consists of two coxal bones. Each coxal bone is formed by the fusion of three bones - ilium, ischium and pubis. At the point of fusion of the above bones is a cavity called acetabulum to which the thigh bone articulates. The two halves of the pelvic girdle meet ventrally to form the pubic symphysis containing fibrous cartilage.

In plants and animals, growth and differentiation are controlled by chemical substances called the hormones. These occur in extremely small quantities. They are transported from the site of their synthesis to the place of action. In animals, these are produced in endocrine glands.

Milk is converted into curd or yogurt by the process of fermentation. Milk consists of globular proteins. During fermentation, the milk sugar (lactose) produces lactic acid. Lactic acid acts on the globular proteins present in the milk and denatures them. This denaturation destroys the tertiary and quaternary structures of proteins and the globular proteins are converted into fibrous proteins thus giving a thick texture to the milk due to coagulation of the proteins.is also called fermentation.

i. Protonemal cell of a Moss- It is haploid (N).
ii. Primary endosperm nucleus (PEN) in dicot- It is triploid (3N).
iii. Leaf cell of a Moss- It is haploid (N).
iv. Prothallus cell of a fern- It is haploid (N).
v. Gemma cell in Marchantia- It is haploid (N).
vi. Meristem cell of Monoco-. It is diploid (2N).
vii. Ovum of a Liverwort- It is haploid (N).
viii. Zygote of a Fern- It is diploid (2N).