Biology

Question 1

Distinguish btwn endocrine and exocrine glands

Answer 1

Exocrine – secreting liquids to the outside (such as tears, sweat, mucus, enzymes or milk); while endocrine – secreting hormones into the bloodstream.

Question 2

Difference between dendrons and axons

Answer 2

Dendrons carry nerve impulses towards the cell body, while a single long axon carries the nerve impulse away from the cell body

Question 3

Types of neurons

Answer 3

1. Sensory neurones
   have long dendrons and transmit nerve impulses from sensory receptors all over the body to the central nervous system.
2. Motor neurones (also called effector neurones)
   have long axons and transmit nerve impulses from the central nervous system to effectors (muscles and glands) all over the body.
3. Interneurones (also called connector neurones or relay neurones)
   are much smaller cells, with many interconnections. They comprise the central nervous system. 99.9% of all neurones are interneurones.

Question 4

The Membrane Potential

Answer 4

• All animal cell membranes contain a protein pump called the Na+K+ATPase. This uses the energy from ATP splitting to simultaneously pump 3 sodium ions out of the cell and 2 potassium ions in.
• These channels are normally closed, but even when closed, they “leak”, allowing sodium ions to leak in and potassium ions to leak out, down their respective concentration gradients.
• The combination of the Na+K+ATPase pump and the leak channels cause a stable imbalance of Na+ and K+ ions across the membrane.

Question 5

Depolarisation and repolarisations

Answer 5

1. Depolarisation. The sodium channels open, causing sodium ions to diffuse in down their gradient, and making the inside of the cell more positive.
2. Repolarisation. The potassium channels open for, causing potassium ions to diffuse out down their concentration gradient, making the inside more negative again.

Question 6

Depolarisation and repolarisations

Answer 6

1. Depolarisation. The sodium channels open, causing sodium ions to diffuse in down their gradient, and making the inside of the cell more positive.
2. Repolarisation. The potassium channels open for, causing potassium ions to diffuse out down their concentration gradient, making the inside more negative again.

Question 7

Action potential

Answer 7

Is the change in the polarity of the memberane where the inside of the membrane is more positive than the outside of the cell

Question 8

How do Nerve Impulses Start?

Answer 8

In living cells they are started by receptor cells. The receptor proteins are sodium channels gated by the appropriate stimulus (directly or indirectly).

Question 9

How are Nerve Impulses Propagated

Answer 9

Once an action potential has started it is propagated (moved) along an axon automatically.

Question 10

How can Nerve Impulses convey strength?

Answer 10

The strength of stimulus is indicated by the frequency of nerve impulses.

a. A weak stimulus (such as dim light, a quiet sound or gentle pressure) will cause a low frequency of nerve impulses along a sensory neurone.
b. A strong stimulus (such as a bright light, a loud sound or strong pressure) will cause a high frequency of nerve impulses along a sensory neurone (up to 100Hz).

Question 11

The speed is affected by 3 factors namely

Answer 11

1. Temperature.
   The higher the temperature, the faster the speed.
2. Axon diameter.
   The larger the diameter, the faster the speed.
3. Myelin sheath. Only vertebrates have a myelin sheath surrounding their neurones. The action potential can therefore jump large distances from node to node, a process that is called saltatory propagation. This increases the speed of propagation dramatically

Question 12

The speed is affected by 3 factors namely

Question 13

What is a refactory period

Answer 13

After an ion channel has opened, it needs a “rest period” before it can open again.

Question 14

Different Types of Synapse

Answer 14

1. Excitatory Ion-channel Synapses.
   -These synapses have neuroreceptors that are sodium (Na+) channels.
   -When the channels open, positive ions diffuse in, causing a local depolarisation called an excitatory postsynaptic potential (EPSP) and creating an action potential.
2. Inhibitory Ion-channel Synapses.
   -These synapses have neuroreceptors that are chloride (Cl-) channels.
   -When the channels open, negative ions diffuse in causing a local hyperpolarisation called an inhibitory postsynaptic potential (IPSP) and inhibiting an action potential.
3. Non-channel Synapses.
   -These synapses have neuroreceptors that are not channels at all, but instead are membrane-bound enzymes.
   -When activated by the neurotransmitter, they catalyse the production of a “messenger chemical” (e.g. Ca2+) inside the cell, which in turn can affect many aspects of the cell’s metabolism.
   -These synapses are involved in slow and long-lasting responses like learning and memory. Typical neurotransmitters are adrenaline, noradrenaline
4. Neuromuscular Junctions.
   -These are the synapses formed between effector neurones and muscle cells.
   -They always use the neurotransmitter acetylcholine, and are always excitatory.
5. Electrical Synapses.
   -In these synapses the membranes of the two cells actually touch, and they share proteins allowing the action potential to pass directly from one membrane to the next without using a neurotransmitter.

Question 15

Define the following terms Spatial and temporal summation

Answer 15

Spatial summation
-Is the summing of postsynaptic potential PSPs from different synapses over the cell body and dendrite tree

Temporal summation
-Is the summing of a sequence of postsynaptic potential PSPs at one synapse over a brief period of time.

Question 16

Differentiate between agonists and antagonists

Answer 16

Drugs that stimulate a synapse are called agonists, and those that inhibit a synapse are called antagonists.

Question 17

Why are Fertilisation and development internal

Answer 17

To limit wastage of gametes and provide protection to the young respectively.

Question 18

Why does breeding coincide with the season cycle

Answer 18

so that birth occurs at a time when environmental conditions are most favourable for growth of young.

Question 19

Use of developing a placenta

Answer 19

enables gaseous exchange and the young to excrete wastes

Question 20

Main features of sexual reproduction

Answer 20

-Fertilisation is internal
-Females go through a sexual cycle known as menstrual cycle
-Sexual cycle is restricted to the breeding season, except in humans and other primates, which are sexually receptive throughout the year
-Young ones are born at an advanced stage.
-There is display of courtship behaviour that leads to mating.
- Development of embryo is internal and completely dependent on the mother for food and protection.
-The young are fed on milk
-Parental care to the young is prolonged

Question 21

Differenciate btw primary and secondary sex organs

Answer 21

-Primary sex organs produce gametes while secondary sex organs do not produce gametes
-Primary sex organs are organs secrete sex hormones while secondary sex organs do not secrete sex hormones
-Primary sex organs are organs development is under the control of FSH and LH while secondary sex organs development is under the control of Oestrogen and progesterone in females and testosterone in males

Question 22

Functions of the penis

Answer 22

-Delivers sperm to the neck of
the cervix, as close to the site of ovulation as possible.

Question 23

Fucntions of the scrotum

Answer 23

-Regulates teste’s temperature at 30C lower than body temperature for proper sperm formation. When cold, the cremaster musclebelevates the testes to absorb heat from the body, this’s reversed at high temperature.

Question 24

Functions of the testes

Answer 24

-Contain seminiferous tubules that produce sperm.
-Produce the male sex hormone
testosterone.

Question 25

Functions of the ovaries

Answer 25

-Are sites for egg production.
-Secrete the hormones oestrogen and progesterone.

Question 26

Functions of the uterus

Answer 26

-Site of implantation of fertilized egg, development of foetus during pregnancy and origin of muscular contractions that precede parturition.

Question 27

Funstions of oviduct (Fallopian tubes)

Answer 27

-The finger-like projections sweep the egg into oviduct.

Question 28

Funstions of the funnels of the oviduct

Answer 28

-Walls are muscular and lined with ciliated epithelium for moving egg from ovary towards uterus.

Question 29

Funtions of the following
1.Prostate gland
2.Seminal vesicles
3.Cowper’s (bulbourethral) gland
4.Epididymis
5.Vas deferens
6.Vagina
7.Clitoris
8.Labia minora and Labia majora

Answer 29

1.Secretes an alkaline fluid that neutralizes the acidic vaginal secretions to avoid reduction in sperm motility at low PH.

2.Secrete an alkaline mucous fluid rich in fructose – the respiratory substrate for sperm motility.

3.Produces a mucous secretion for lubricating the penis during intercourse and neutralizing the acidity of any remaining urine.

4.
-Sperm maturation site (1-10 days).
-Stores spermatozoa (up to 4wks)

5.Stores sperm (up to many months) before ejaculation

6.Passage for menstrual flow, receptacle for penis during coitus and lower part of birth canal.

7.Tactile stimulation excites the female sexually during intercourse.

8.Produce a lubricant mucus secretion during intercourse and protect the clitoris from abrasion.

Question 30

Spermaotogenesis

Answer 30

Multiplication phase
-At puberty, diploid germinal Epithelial cells (primordial germ cells) of seminiferous tubules undergo repeated mitotic divisions to form a number of diploid spermatogonia.

Growth phase
-Each spermatogonium increases in size and becomes a primary spermatocyte.

Maturation phase
-Each primary spermatocyte undergoes the first meiotic division to form two haploid secondary spermatocytes, which undergo second meiotic division to form four haploid spermatids, connected to each other by cytoplasm.

Spermiogenesis
-The spermatids get embedded into sertoli cells (loosely called “nurse cells”) to be transformed into sperm by:
(i) Losing part of cytoplasm
(ii) Condensation of nucleus into head.
(iii) Formation of flagellated tail.
The mature spermatozoa (sperms) finally detach from sertoli cells and are released into the lumen of seminiferous tubules.

Question 31

Oogenesis

Answer 31

Multiplication phase
-During embryonic development, diploid oogonia (germinal epithelial cells of ovary) undergo repeated mitotic divisions to increase in number.

Growth phase
-Some oogonia undergo mitosis to form primary oocytes, which remain at prophase I of meiosis, while the rest (now called follicle cells/granulosa cells) enclose the primary oocytes.

Maturation phase
-At puberty, granulosa cells multiply to form primary follicle & other cell layers around the primary oocyte.
-The primary oocyte undergoes meiosis up to metaphase II only to form a secondary oocyte and 1st polar body
-The primary follicle develops to form fluid filled secondary follicle and later Graafian follicle, which enclose secondary oocyte & 1st polar body.
-At fertilization, the secondary oocyte completes meiosis II to form a large ootid (ovum) and second polar body.
-The first polar body also undergoes meiosis at the same time to form two small polar bodies.
-All the three polar bodies degenerate and only one functional egg remains

Question 32

Explain the significance of formation polar bodies during oogenesis

Answer 32

-Polar bodies take the extra chromosomes resulting from meiosis in order for the ovum to carry haploid number of chromosomes.
-The unequal cytoplasmic division results into the formation of a large egg with the cytoplasm containing sufficient yolk for the development of the embryo.

Question 33

Similarities between spermatogenesis and oogenesis in humans

Answer 33

-Both begin with diploid germinal epithelial cells —Mitosis and meiosis are involved in both
-Both yield haploid gametes
-Both occur in gonads

Question 34

Outline the hormonal control of spermatogenesis

Answer 34

-Interaction of hormones from the hypothalamus and anterior pituitary gland working together controls
spermatogenesis.
-From the hypothalamus, gonadotrophin-releasing hormone (GnRH) stimulates the anterior pituitary gland to secrete two gonadotrophins (gonad stimulating hormones), i.e. follicle stimulating hormone (FSH) and
luteinising hormone (LH)/interstitial cell stimulating hormone (ICSH).
-FSH stimulates spermatogenesis by causing sertoli cells to complete the development of spermatozoa from
spermatids.
FSH also causes sertoli cells to release a peptide hormone inhibin that specifically inhibits FSH secretion.
-LH (ICSH) stimulates the leydig cells (interstitial cells) of the testes to secrete testosterone.
- Testosterone stimulates the growth and development of germinal epithelial cells (spermatogonia) to form sperm, and also works with FSH to stimulate the sertoli cells.
-However, increased testosterone level inhibits the secretion of GnRH and LH.