Birds have undergone many structural adaptations to suit their aerial life. Some of these adaptations are as follows.
(i) Streamlined body for rapid and smooth movement
(ii) Covering of feathers for insulation
(iii) Forelimbs modified into wings and hind limbs used for walking, perching, and swimming
(iv) Presence of pneumatic bones to reduce weight
(v) Presence of additional air sacs to supplement respiration
Which of the following is not correct?
(a) Robert Brown discovered the cell.
(b) Schleiden and Schwann formulated the cell theory.
(c) Virchow explained that cells are formed from pre-existing cells.
(d) A unicellular organism carries out its life activities within a single cell.
Cell is the basic unit of life. Discuss in brief.
Name two cell-organelles that are double membrane bound. What are the characteristics of these two organelles? State their functions and draw labelled diagrams of both.
New cells generate from (a) bacterial fermentation (b) regeneration of old cells (c) pre-existing cells (d) abiotic materials
Describe the important steps in muscle contraction.
List the hormones secreted by the following:
(a) Hypothalamus
(b) Pituitary
(c) Thyroid
(d) Parathyroid
(e) Adrenal
(f) Pancreas
(g) Testis
(h) Ovary
(i) Thymus
(j) Atrium
(k) Kidney
(l) G-I Tract
Match the following (a) Cristae (i) Flat membranous sacs in stroma (b) Cisternae (ii) Infoldings in mitochondria (c) Thylakoids (iii) Disc-shaped sacs in Golgi apparatus
Bile juice contains no digestive enzymes, yet it is important for digestion. Why?
What is a mesosome in a prokaryotic cell? Mention the functions that it performs.
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