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 called pia mater. The brain can be divided into three major parts. (i) Forebrain (ii) Midbrain and (iii) Hindbrain.

The human heart is a four-chambered organ two atria and two ventricles. The two auricles are partitioned by a septum into a right auricle receiving only deoxygenated blood and a left auricle receiving only oxygenated blood. Due to further advancement in the human heart, the ventricle is completely partitioned into the right ventricle and left ventricle to prevent mixing of deoxygenated and oxygenated blood.

a. Blood contains RBCs and hence can transport gases. Lymph doesn't contain RBCs and cannot transport gases. Lymph mainly contains WBCs and play a role in the immune system of the body.
b. The Open Circulatory System is a system in which fluid (called hemolymph) in a cavity called the hemocoel bathes the organs directly with oxygen and nutrients and there is no distinction between blood and interstitial fluid this combined fluid is called hemolymph or haemolymph. The cardiovascular systems of humans are closed, meaning that the blood never leaves the network of blood vessels.
c. Systole is the contraction of heart muscle and diastole is the dilatation of the heart muscle.
d. Each peak in the ECG is identified with a letter from P to T that corresponds to a specific electrical activity of the heart. The P-wave represents the electrical excitation (or depolarisation) of the atria, which leads to the contraction of both the atria. The QRS complex represents the depolarisation of the ventricles, which initiates the ventricular contraction. The contraction starts shortly after Q and marks the beginning of the systole. The T-wave represents the return of the ventricles from excited to normal state (repolarisation). The end of the T-wave marks the end of systole.

The synovial joints are freely movable joints. The presence of synovial fluid in the synovial cavity makes this joint movable. This fluid lubricates the joint for free and easy movement. The articulating bones provide considerable movement but articulating surfaces are kept in close contact by a fibrous capsule. The examples of synovial joints are:
i. Ankle joint and
ii. Shoulder joint etc.

i. It promotes growth and elongation of roots and stems and many fruits.
ii. In many plants, indole acetic acid promotes cell division and induces apical dominance.
iii. It also induces parthenocarpy.

Small Molecular Weight Biomolecules: Lactic acid, simple sugars, pentoses, hexoses, lipids, fatty acids, amino acids and nucleotides.
Sugar and cotton, as well as biotechnological industries, manufactures the compounds by isolation.