Exam practice

Blood is a connective tissue because, like other connective tissues, its cells (red cells, white cells, platelets) are spread out in a large amount of matrix, and it links all the parts and systems of the body by carrying materials between them. Its matrix, the plasma, is a liquid, so it is a liquid connective tissue.

The tip of the stem holds the apical meristem, whose dividing cells make the stem longer. When the tip is cut off, the apical meristem is removed, so no new cells are added at the top and the stem stops growing in height. (The side buds then grow into branches instead.)

Lalupate has laticiferous tissue, special cells and tubes that contain a milky liquid called latex. When a leaf is broken, these tubes are cut and the latex oozes out. It helps seal the wound and protects the plant.

Xylem is permanent because its cells have stopped dividing and have a fixed shape and job. It is complex because it is made of more than one kind of cell (vessels, tracheids, xylem fibers and xylem parenchyma, some dead and some living) working together as one unit to carry water and minerals.

The activities a living thing must carry out to stay alive and to keep its kind going are called life processes. Examples:

• Nutrition: taking in or making food (a plant makes food by photosynthesis; we eat).
• Respiration: breaking down food to release energy.
• Circulation: carrying materials around the body (blood in animals, xylem and phloem in plants).
• Excretion: removing waste products (we pass urine and breathe out carbon dioxide).
• Reproduction: producing young of the same kind.

In a unicellular organism, one cell does all of these; in a multicellular organism, special tissues, organs and systems do them.

Plant tissues (as in Figure 5.2):

• Meristematic: apical (tips of stem and root), lateral (cambium), intercalary (base of internodes).
• Permanent: simple (parenchyma, e.g. potato flesh; collenchyma, e.g. leaf stalks; sclerenchyma, e.g. coconut husk), complex (xylem, e.g. wood; phloem, e.g. bast), special (glandular, e.g. tulsi oil glands; laticiferous, e.g. lalupate).

Animal tissues (as in Figure 5.8):

• Epithelial: squamous (lining of blood vessels), cuboidal (kidney tubules), columnar (lining of the intestine), glandular (sweat glands).
• Muscular: skeletal (biceps), cardiac (heart wall), smooth (stomach wall).
• Connective: soft (areolar under the skin; adipose; tendons, ligaments), hard (bone, cartilage), fluid (blood, lymph).
• Nervous: neurons and neuroglia (brain, spinal cord, nerves).

Meristematic tissue is a plant tissue made of cells that keep dividing. Its cells have thin walls, a large nucleus, dense cytoplasm and few or no vacuoles, and are packed together with no spaces between them. It is found in the growing regions and makes the plant grow. Three kinds, by position (draw as in Figure 5.4):

• Apical meristem, at the tips of the stem and root: makes them longer.
• Lateral meristem (cambium), in a ring along the sides of the stem and root: makes them thicker.
• Intercalary meristem, at the base of the internodes: makes the internodes longer.

A permanent tissue is made of cells that have lost the power to divide and have taken a fixed shape, size and job. Its cells may be living or dead. There are three kinds:

1. Simple permanent tissue, made of one kind of cell: parenchyma (stores and makes food; potato), collenchyma (strength with flexibility; leaf stalks) and sclerenchyma (hardness; coconut husk, seed coats).
2. Complex permanent tissue, made of several kinds of cell working together: xylem (carries water and minerals up; wood) and phloem (carries food; bast).
3. Special tissue, which makes or stores particular substances: glandular tissue (oils, resin, nectar; tulsi, pine) and laticiferous tissue (latex; lalupate, pipal, rubber).

Draw them as in Figure 5.5: parenchyma as rounded cells with thin walls, a nucleus, a vacuole and spaces between them; collenchyma as many-sided cells with thick corners and no spaces; sclerenchyma as cells with very thick walls and a tiny empty lumen.

• Parenchyma: stores food; makes food by photosynthesis (as chlorenchyma); helps water plants float (as aerenchyma).
• Collenchyma: gives mechanical strength and flexibility to young stems and leaf stalks; some make food.
• Sclerenchyma: makes the plant hard, strong and rigid; forms the hard coverings of seeds and nuts.

1. Covers and protects the body and its organs from injury, germs and drying out (skin).
2. Lines the tubes and cavities inside the body (blood vessels, food canal, windpipe).
3. Secretes substances such as mucus, enzymes, sweat and hormones (glandular epithelium).
4. Absorbs substances, such as digested food in the intestine (columnar epithelium).
5. Excretes wastes (kidney tubules) and lets substances pass by filtering and diffusion (squamous epithelium of the air sacs and capillaries).
6. Ciliated epithelium of the windpipe sweeps out dust and mucus.

• i.It shows the vascular (complex permanent) tissues, xylem (left) and phloem (right), cut lengthwise.
• ii.A: xylem vessel; B: sieve tube; C: companion cell; D: sieve plate.
• iii.Xylem carries water and minerals from the roots up to the leaves and all other parts; phloem carries food made in the leaves to all parts of the plant, upwards and downwards.
• iv.Without them, the leaves would get no water for photosynthesis and the roots, flowers and fruits would get no food. Xylem also makes the plant strong (wood), so it can stand tall and reach the light.

• i.A: skeletal (striped) muscle; B: cardiac muscle; C: smooth (unstriped) muscle.
• ii.A: attached to the bones of the arm (biceps); B: the heart; C: the stomach (or intestine, or blood vessels).
• iii.A: moves the bones at will, such as bending the arm; B: contracts rhythmically to pump blood (the heartbeat); C: pushes food along the food canal by slow, involuntary contractions.

• i.A neuron (nerve cell).
• ii.a: dendrites; b: axon (with its myelin sheath and axon terminals); c: cell body (cyton).
• iii.a: dendrites receive messages from other neurons or sense cells and carry them to the cell body. b: the axon carries messages away from the cell body to the next neuron, a muscle or a gland; its myelin sheath speeds the message up. c: the cell body holds the nucleus and keeps the neuron alive; messages pass through it from the dendrites to the axon.

The cerebrum is the part of the brain that creates consciousness, thought, memory and awareness, and controls the other parts of the brain. When it is badly injured, these functions stop, so the person loses consciousness and may remain unconscious, in a coma.

It is a reflex action. The heat stimulates receptors in the skin; the impulse goes along a sensory nerve to the spinal cord, where a connecting neuron passes it straight to a motor nerve; the motor nerve makes the arm muscle contract and pull the hand away. Because the message doesn’t have to go to the brain and wait for a decision, the response is very fast and protects the hand from a burn.

The cerebellum coordinates the muscles’ movements, times them, and keeps the body balanced while we walk, run or stand; it also keeps muscle tone and posture. When it is injured, this coordination fails: movements become shaky and unbalanced, and the person staggers or falls, as someone who has drunk too much alcohol does.

In a reflex action, the message from the receptor travels along a sensory nerve to the spinal cord, and it is there, in the gray matter, that a connecting neuron passes it to a motor nerve, which carries the response to the muscle. The brain is not needed for the response. Since the spinal cord receives the message and sends out the response, it is called the center of reflex action.

Draw it as in Figure 5.19: the large, folded cerebrum on top; the cerebellum at the back underneath it, with fine parallel folds; the pons and the medulla oblongata below, leading down into the spinal cord. Label each part.

The medulla oblongata, the lowest part of the brainstem, controls the involuntary actions that keep us alive:

1. It regulates breathing (the rate and depth of respiration).
2. It controls the heartbeat.
3. It controls the narrowing and widening of blood vessels, and so the blood pressure.
4. It controls reflexes such as vomiting, coughing, sneezing and swallowing.
5. It controls the secretion of saliva and digestive juices.

It also passes messages between the spinal cord and the rest of the brain. Because breathing and the heartbeat depend on it, an injury to it can cause death at once.

The autonomic nervous system controls the involuntary actions of the internal organs, such as the heart, lungs, kidneys, stomach, intestine, blood vessels and glands, all the time, asleep or awake, without our will. It has two parts that work against each other:

• the sympathetic system prepares the body for an emergency: it speeds up the heartbeat and breathing, raises the blood pressure, widens the pupils and slows digestion;
• the parasympathetic system brings the body back to rest: it slows the heartbeat and breathing, lowers the blood pressure, narrows the pupils and speeds up digestion.

Diagram: draw the spinal cord with nerves from it to the eye, heart, lungs, stomach and intestine; on one side mark the effects of the sympathetic system, on the other those of the parasympathetic system (the organs in the widget above show them).

When the finger touches a hot object:

1. Receptors (nerve endings) in the skin sense the heat and start an impulse.
2. A sensory nerve carries it to the spinal cord.
3. In the spinal cord, a connecting neuron passes it to a motor nerve.
4. The motor nerve carries the impulse to the muscles of the arm (the effector).
5. The muscles contract and the hand is pulled away.

This path, receptor → sensory nerve → spinal cord → motor nerve → effector, is the reflex arc. The message reaches the brain only afterwards, and then we feel the pain.

The nervous system is the system of the brain, spinal cord and nerves that receives information about changes inside and outside the body, makes sense of it, and controls and coordinates the activities of all the organs. Its three parts:

1. Central nervous system: the brain and spinal cord; the control center.
2. Peripheral nervous system: the 12 pairs of cranial nerves and 31 pairs of spinal nerves, which link the CNS with the sense organs, muscles and glands.
3. Autonomic nervous system: sympathetic and parasympathetic; controls the involuntary actions of the internal organs.

Small brain (cerebellum): coordinates muscular movements; keeps the body balanced; keeps muscle tone and posture; makes voluntary movements smooth.

Large brain (cerebrum): thinking, memory, intelligence, imagination and consciousness; speech; makes sense of sight, hearing, smell, taste and touch; controls voluntary actions and the other parts of the brain.

Spinal cord: carries messages between the brain and the body; is the center of reflex actions.

A neuron (nerve cell) is the structural and functional unit of the nervous system, a cell that carries messages (nerve impulses). Draw it as in Figure 5.13.

• Dendrites: receive messages from other cells and carry them towards the cell body.
• Cell body (cyton): holds the nucleus; keeps the neuron alive; passes the message on to the axon.
• Axon: carries messages away from the cell body.
• Myelin sheath: insulates the axon and makes the message travel faster.
• Axon terminals: pass the message to the next neuron, a muscle or a gland.

A reflex action is a quick, automatic, involuntary response to a stimulus, made without thinking, and controlled mostly by the spinal cord. It protects the body from harm. Examples: pulling the hand away from a hot object or a thorn; blinking when something comes towards the eye; the knee jerk; sneezing and coughing; putting the hands out when we slip. The message travels along a reflex arc: receptor → sensory nerve → spinal cord (connecting neuron) → motor nerve → effector (muscle or gland).

• i.A: cerebrum; B: cerebellum; C: medulla oblongata.
• ii.A: thinking, memory, speech, the senses, consciousness and voluntary actions. B: balance, posture and the coordination of movements. C: breathing, heartbeat, blood pressure, and reflexes such as swallowing, coughing, sneezing and vomiting.
• iii.Breathing and the heartbeat can stop, so an injury to the medulla oblongata can kill a person almost at once.

The pancreas works both as an exocrine gland and as an endocrine gland. It makes pancreatic juice, full of enzymes, which goes through a duct to the duodenum; and its islets of Langerhans release the hormones insulin and glucagon straight into the blood. Since it has both kinds of secretion, it is a mixed gland.

The pituitary makes stimulating hormones that control the working of the other endocrine glands, such as the thyroid, the adrenal glands and the gonads, as well as growth hormone. Because it coordinates and controls the other glands, it is called the master gland.

A hormone is a chemical made in an endocrine gland, but it does its work somewhere else: it is carried by the blood to particular cells and organs, often far away, and changes what they do. Since it carries a “message” from the gland to its target, it is called a chemical messenger.

Insulin lowers the blood sugar: it helps the cells take in glucose and the liver store it. Glucagon raises the blood sugar: it makes the liver release its stored sugar into the blood. Their effects are opposite, so they are called antagonistic hormones; together they keep the blood sugar steady.

A catalyst is a substance that speeds up a chemical reaction without being used up in it. Enzymes are proteins made by living cells that speed up the chemical reactions of the body, such as the digestion of food, without being used up. Since they are catalysts made by and working in living things, they are called biological catalysts.

A gland is a cell or an organ that makes a useful substance (a secretion, such as a hormone, an enzyme or a juice) and releases it. Chart (Figure 5.22):

• Exocrine (duct) glands: sweat glands, salivary glands, tear glands.
• Endocrine (ductless) glands: pituitary, thyroid, parathyroid, adrenal.
• Mixed glands: pancreas, gonads (testes, ovaries).

Plant hormones are chemical substances made in small amounts in certain parts of a plant (mainly the growing tips) that travel to other parts and control its growth and development. They are not nutrients but chemical messengers. They control how a plant grows taller and thicker, bends towards light, forms roots and shoots, flowers, sets and ripens fruit, and drops its leaves. Examples: auxin (cell lengthening, phototropism, apical dominance), gibberellin (stem lengthening), cytokinin (cell division), ethylene (ripening and leaf fall) and brassinosteroids.

Draw a body outline as in Figure 5.23 and mark: the pituitary at the base of the brain; the thyroid in the neck, with the parathyroids behind it; the adrenals on top of the kidneys; the pancreas behind the stomach; the ovaries in the lower abdomen (or the testes in the scrotum).

The pituitary gland is a pea-sized endocrine gland hanging from the base of the brain, inside the skull. It makes growth hormone, which controls the growth of the body, and stimulating hormones, which control other endocrine glands such as the thyroid, the adrenals and the gonads; so it is called the master gland. Too little growth hormone in childhood causes dwarfism (very short height); too much causes gigantism (very great height).

Auxin, gibberellin, cytokinin, ethylene and brassinosteroids. (Another important one, abscisic acid, helps a plant survive dry spells by closing its stomata.)

1. In tissue culture, auxin and cytokinin are added in the right balance to grow many disease-free plantlets quickly: more auxin forms roots, more cytokinin forms shoots.
2. Auxin helps cuttings to root and fruits to set.
3. Gibberellin makes fruits such as grapes bigger and helps seeds sprout.
4. Ethylene ripens fruits evenly for the market.
5. Hormones help produce good-quality and off-season vegetables and fruits.

They must be used in small, correct amounts: too much on food crops can harm people’s health.

The pancreas is a long, leaf-shaped gland, about 12–15 cm long, behind the stomach, in the loop of the duodenum. Draw it lying across the abdomen with its head in the curve of the duodenum (Figure 5.23). It is a mixed gland:

• Exocrine part: makes pancreatic juice with digestive enzymes, which flows through the pancreatic duct into the duodenum and helps digest food.
• Endocrine part: the islets of Langerhans release insulin, which lowers blood sugar, and glucagon, which raises it.

Too little insulin causes diabetes; too much causes very low blood sugar, with shaking, confusion and fainting.

• Too much growth hormone in childhood: gigantism, the person grows unusually tall.
• Too much thyroxine: the metabolism speeds up: heavy sweating, hunger, loss of weight, nervousness and bulging eyes.
• Too much parathormone: calcium leaves the bones, which become weak, and kidney stones may form.
• Too much adrenaline: high blood pressure.
• Too much insulin: blood sugar falls too low: anxiety, shaking, fainting, and in severe cases coma.

The two systems work together to control the body. The hypothalamus, a part of the brain, controls the pituitary, which in turn controls the thyroid, adrenals and gonads; so the nervous system controls much of the glandular system. For example, when we are frightened, the sympathetic nerves make the adrenal glands release adrenaline, which keeps the heart racing and the blood sugar high so the body can face the danger. Hormones also affect the nervous system: thyroxine is needed for the normal growth of the brain, and a child without enough of it develops mental disabilities. Nerves give fast, short-lived control; hormones give slower, longer-lasting control.

• a.A: pituitary; B: thyroid; C: parathyroid; D: adrenal; E: pancreas; F: ovary.
• b.Each gland’s hormone and one of its functions are in the table below.
• c.Parathormone: too little of it lowers the calcium in the blood and causes tetany (muscle spasms).