Which of the following is the main thinking part of the human brain?

The correct answer is B, Fallopian tube. In human beings the sperm meets and fuses with the egg inside the fallopian tube, also called the oviduct.

The ovary releases one egg in a month, and the funnel shaped mouth of the fallopian tube collects it. Sperms swim up from the vagina through the cervix and the uterus into the tube, and fusion usually happens in its wider upper part. The fertilised egg, now a zygote, begins to divide as the tube's lining pushes it along, and reaches the uterus in a few days as a ball of cells that implants in the thick uterine wall and grows there with the help of the placenta.

Option A is wrong because the uterus is where the embryo implants and develops, after fertilisation. Option C is wrong because the ovary only makes and releases the egg. Option D is wrong because the vagina is the passage the sperms enter through.

Exam tip: egg made in the ovary, fertilised in the fallopian tube, developed in the uterus.

The correct answer is B, regeneration. Hydra, starfish and planaria can all grow a lost or cut off part of the body back into a whole animal, and that ability is called regeneration.

Regeneration works because these animals keep a large number of unspecialised cells that can divide and turn into any kind of tissue. A planaria cut into pieces gives a complete worm from each piece, a starfish grows a new arm and can rebuild itself from an arm with part of the central disc, and a piece of Hydra grows the missing mouth and tentacles. It is not the normal way these animals reproduce; it is a repair power that can also produce new individuals.

Option A is wrong because sporulation is the making of spores, seen in fungi like Rhizopus. Option C is wrong because budding is shown by Hydra and yeast but not by starfish or planaria. Option D is wrong because fragmentation is seen in filamentous algae such as Spirogyra.

Exam tip: regeneration in Hydra, planaria and starfish; budding in Hydra and yeast; fragmentation in Spirogyra; spore formation in Rhizopus.

The correct answer is B, Hydra. Hydra is the one animal in the list that reproduces both by budding and by regeneration.

In budding, a bulge grows out from the body wall of the parent Hydra, develops a mouth and tentacles, and then breaks off as a small independent Hydra. In regeneration, a piece cut from the body grows the missing parts back and becomes a complete animal, because Hydra keeps a large store of unspecialised cells that can turn into any tissue. Both are forms of asexual reproduction, so the young are copies of the parent.

Option A is wrong because Planaria is the classic example of regeneration alone and does not bud. Option C is wrong because Amoeba divides into two by binary fission. Option D is wrong because yeast reproduces only by budding, and it is a fungus, not an animal.

Exam tip: Hydra shows budding and regeneration, Planaria only regeneration, Amoeba binary fission, Plasmodium multiple fission.

The correct answer is A, Cellulose and Pectin. Collenchyma cells lay down extra cellulose and pectin at the corners of their walls, which makes the tissue strong and yet flexible.

Collenchyma is a simple permanent tissue of plants, found just under the epidermis in the stems and leaf stalks of dicot plants and in the midrib of a leaf. Its cells are living and elongated, thickened unevenly at the corners, with almost no space between them. This uneven thickening lets a young shoot or a leaf stalk bend in the wind without breaking, and it is what allows climbing stems to twist.

Option B is wrong because lignin thickens sclerenchyma and cutin waterproofs the epidermis. Option C is wrong because chitin is found in fungal walls and insect skeletons, not in plant tissue. Option D is wrong because suberin is deposited in cork cells.

Exam tip: parenchyma has thin cellulose walls, collenchyma adds cellulose and pectin at the corners and stays flexible, sclerenchyma is lignified, dead and rigid.

The correct answer is B, Papaya. Papaya is raised from seed, so it is not multiplied by vegetative propagation the way the other three plants are.

Vegetative propagation means growing a new plant from a vegetative part of the parent, such as a stem, root, leaf or bud, without seeds. Because no seed is involved, the new plant is a copy of the parent and it also fruits sooner. Papaya has plenty of viable seed, and its soft unbranched stem does not strike roots from a cutting, so nurseries sow seed instead.

Option A is wrong because rose is the standard example of a plant grown from stem cuttings. Option C is wrong because banana is grown from suckers that come up from the underground stem, as its seeds are sterile. Option D is wrong because orange and other citrus plants are multiplied by budding and grafting on a rootstock.

Exam tip: cuttings give rose and sugarcane, suckers give banana, grafting and budding give citrus and mango, while papaya comes from seed.