gr 12 life sciences: paper 1 - the...

GR 12 LIFE SCIENCES:

PAPER 1

Questions.................................................. 1

Answers .................................................... 7

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HUMAN REPRODUCTION

QUESTION 1

Study the representation below of part of sexual reproduction in humans and answer the questions that follow.

1.1 Identify the cycle represented by A.

1.2 Identify the structures that are numbered from 1 to 4.

1.3 Which hormone:

1.3.1 was involved in the development of structure 1?

1.3.2 is secreted by structure 1?

1.3.3 ensures the development of structure 3?

1.3.4 is secreted by structure 3?

1.4.1 Identify the part that is numbered 5. 1.4.2 How is the part numbered 5 structurally adapted to ensure that the structure

numbered 2 will move towards the uterus?

1.5.1 Identify the structure numbered 6. 1.5.2 Which process is represented by B? 1.5.3 Identify the structure numbered 7. 1.5.4 What is the chromosome number of the parts that are numbered 2, 4, 5, 6,

and 7 respectively?

1.6.1 Identify the structure numbered 8. 1.6.2 Which type of cell division has ensured that the structure mentioned in

Question 1.6.1 develops from structure 7? 1.6.3 Identify the structure numbered 9. 1.6.4 Describe the development and structure of the stage labelled 9, until it is ready

for implantation.

1.7.1 Identify the part numbered 10. 1.7.2 Which changes occurred in the part mentioned in Question 1.7.1 to

prepare it for implantation? 1.7.3 Which hormones were responsible for these changes mentioned in Question 1.7.2? 1.7.4 Identify the process represented by C. 1.7.5 Identify the structure numbered 11. 1.7.6 These structures, mentioned in Question 1.7.5, later form part of the ......

1.8 What will happen to each of the following should fertilisation not occur?

1.8.1 progesterone level 1.8.2 corpus luteum

1.8.3 menstrual cycle 1.8.4 follicle development

1.9 What happens to each of the following if fertilisation does occur?

1.9.1 progesterone level 1.9.2 corpus luteum

1.9.3 menstrual cycle 1.9.4 follicle development







A B

C

1

2

3

4

5

6

7

8

9

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11

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QUESTION 2

Study the diagram illustrating a menstrual cycle below and answer the questions that follow.

2.1 On which day does ovulation take place? 2.2 Between which days does menstruation take place? 2.3 State ONE function of FSH during the menstrual cycle. 2.4 Describe the functional relationship between progesterone and FSH. 2.5 Account for the change in the thickness of the endometrium between day 14 and day 21. 2.6 Did fertilisation take place within the 28-day cycle illustrated in the graph? 2.7 Give FOUR reasons for your answer in Question 2.6.

RESPONDING TO THE ENVIRONMENT:

HUMANS

QUESTION 3

Study the drawing below of a section through a part of the human central nervous system and answer the questions that follow. 3.1 Identify the parts numbered 1 to 13. 3.2 What are the functions of the parts numbered 1 and 5 respectively? 3.3 Write down the NUMBER of the part responsible for: 3.3.1 the control of the permeability of the renal collecting ducts 3.3.2 the connection between the two cerebral hemispheres 3.3.3 serving as a pathway for nerve impulses to and from the brain 3.3.4 control of heart rate 3.3.5 the ability to play chess 3.3.6 peristaltic control 3.3.7 maintenance of muscle tone and balance 3.3.8 protective reflexes 3.4 In a lumbar puncture, fluid is extracted from the central canal of the spinal cord

(e.g. when a doctor confirms meningitis in a patient). What is this fluid called? 3.5 Apart from the central canal, name TWO other locations in the nervous system

where the fluid mentioned in Question 3.4 may occur. 3.6 List FIVE functions of the fluid mentioned in Question 3.4. 3.7 Write down the NUMBERS of two parts where grey matter appears on the outside

and white matter on the inside.

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Hypophysis hormone levels

Development of follicle

Ovarian hormone levels

Thickness ofendometrium

oestrogen progesterone

Days

Hormonal regulation of the female reproductive cycle

FSH LH

0 7 14 21 28

1 2 3

4

5

6

7

8

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1 2

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910 11

12 X

Y

A B

QUESTION 4

Study the representation of a reflex arc below and answer the questions that follow.

4.1 Define the concept reflex arc.

4.2 What is meant by the term reflex reaction?

4.3 In the reflex arc above, name the: 4.3.1 stimulus

4.3.2 receptor

4.3.3 effector

4.4 Describe AND give an example of 4.4.1 natural/unconditioned reflexes 4.4.2 learnt/conditioned reflexes

4.5 Identify the parts numbered 1 to 12.

4.6 An injury occurs. Explain which neuron is damaged and what the effect will be if the

injury takes place at 4.6.1 X 4.6.2 Y 4.7 The diagrams labelled A to D below show what happens in a reflex action.

4.7.1 Arrange the drawings in the correct sequence to represent what happens

during the reflex action. 4.7.2 Fully describe this reflex action.

QUESTION 5

Study the representation of a section through the human eye and answer the questions that follow.

5.1 Write down the NUMBERS only of the respective parts comprising the: 5.1.1 outer fibrous layer 5.1.2 middle vascular layer 5.1.3 inner retina 5.2 Identify the parts numbered 1 to 15. 5.3 List the function(s) AND the adaptation(s) of the following parts: 5.3.1 sclera 5.3.2 cornea

5.3.3 choroid 5.3.4 ciliary body

5.3.5 lens 5.3.6 iris

5.3.7 pigment layer of retina 5.3.8 nervous tissue layer of retina

5.3.9 optic nerve 5.3.10 vitreous humour 5.4 Distinguish between the: 5.4.1 yellow spot and blind spot 5.4.2 aqueous humour and vitreous humour 5.5 Study the accompanying representations of a rod (A) and

a cone (B) and answer the questions that follow. 5.5.1 In which layer of the eye do you find rods and cones? 5.5.2 What is the collective name for rods and cones? 5.5.3 What is the collective function of rods and cones? 5.5.4 State the specific function of: (a) rods (b) cones 5.5.5 Which part of the retina:

(a) contains no rods?

(b) contains neither rods nor cones?

(c) contains only cones?

A B C D

1

2

3

4

5

6

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10

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QUESTION 6

Study the drawings below and answer the questions that follow. 6.1 Which phenomenon is illustrated in these drawings?

6.2 Explain this phenomenon mentioned in Question 6.1.

6.3 In which drawing, A or B, is the eye: 6.3.1 in the accommodated state where the curvature of the lens changes to

focus incoming light rays on the retina to form a clear image? 6.3.2 in the normal unaccommodated state where objects can be observed

without any adaptations and form a clear image on the retina? 6.4 Study the following drawings of the parts of the eye that play a role in eye

accommodation and answer the questions that follow.

6.4.1 Identify the parts numbered 1 to 3. 6.4.2 Explain, with reference to the parts identified in Question 6.4.1, how eye accommodation takes place to obtain a sharp, focused image on the retina

for objects closer than 6 m.

6.5 Why would a person who has had no specific eye defects, probably need glasses

with convex lenses after the age of 40?

6.6 Study the diagrams below that show changes in the shape of the lens and answer

the questions that follow. Write down the LETTER only of the diagram that illustrates the adaptation in each

of the following cases. Explain your answer in each case.

6.6.1 A teacher checking a learner’s homework in his book. 6.6.2 A cricket player watching a ball being bowled towards him. 6.6.3 A person watching a violinist from the back of a hall. 6.6.4 A mother watching a toddler riding a tricycle down the road.

QUESTION 7

Study the representation of the human ear below and answer the questions that follow.

7.1 Identify the three parts of the ear, labelled A, B and C respectively.

A

Sh

ap

e o

f le

ns

B

Sh

ap

e o

f le

ns

C

Sh

ap

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f le

ns

D

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f le

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1

2 6

7

8

93 45

1012

14

13

11

A B C

15

A B

1

2

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7.2 What are the receptors responsible for hearing and balance in the ear called?

7.3 Identify AND give the function of the parts numbered 1 and 2 respectively.

7.4 Identify the ossicles numbered 3, 4 and 5 respectively.

7.5 Give the function of the ossicles.

7.6 Identify AND give the function of the membrane-covered openings to the middle

ear, numbered 6, 7 and 8 respectively.

7.7 Identify AND give the function of the part numbered 15.

7.8.1 The vestibular apparatus consists of the parts numbered 9 and 10 respectively.

Identify these two parts. 7.8.2 Name the mechanoreceptors that are found in the part numbered 9 AND give

its function. 7.8.3 Name the two membranous sacs that are included in the part numbered 10. 7.8.4 Name the mechanoreceptors found in the part numbered 10 AND give their

function.

7.9.1 Identify the part numbered 11. 7.9.2 Identify the functional unit of hearing situated inside part numbered 11. 7.10.1 Identify the parts numbered 12 and 13 respectively. 7.10.2 Identify AND give the functions of the part numbered 14.

QUESTION 8

Study the diagram of a part of the human inner ear and answer the questions that follow.

8.1 Identify the membranous sacs of the

vestibular apparatus labelled A and B

respectively.

8.2 Identify the part of the semicircular canals

that is numbered 1.

8.3.1 Identify the mechanoreceptors numbered 2.

8.3.2 Describe the structure of the receptors mentioned in Question 8.3.1. 8.3.3 State the function of the receptors mentioned in Question 8.3.1. 8.3.4 Explain how the receptors perform the function mentioned in Question 8.3.3.

8.4.1 Identify the mechanoreceptor numbered 3. 8.4.2 Describe the structure of the receptors mentioned in Question 8.4.1. 8.4.3 State the function of the receptors mentioned in Question 8.4.1. 8.4.4 Explain how the receptors perform the function mentioned in Question 8.4.3.

HUMAN ENDOCRINE SYSTEM

QUESTION 9

Study the diagram of the endocrine glands in the human body below and answer the questions that follow.

9.1 Identify the glands numbered 1 to 6 respectively. 9.2 Answer the following questions about the gland numbered 1: 9.2.1 Describe the location of this gland. 9.2.2 Which part of the brain controls the hormone secretions of this gland? 9.2.3 Describe the relationship between the hypothalamus and the hypophysis. 9.2.4 Draw a table to show the FIVE hormones secreted by the anterior

lobe of this gland, AND the function(s) of each.

1

2

3

4

5

6

1

23

B

A


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9.2.5 Which growth disorder is caused by:

(a) hyposecretion of growth hormone (STH) in children?

(b) hypersecretion of growth hormone (STH) in children?

(c) hypersecretion of growth hormone (STH) in adults? 9.2.6 Name the hormone released by the posterior lobe of this gland AND give

the function of the hormone. 9.3 Answer the following questions about the gland numbered 2:

9.3.1 Describe the location of this gland. 9.3.2 Which hormone is secreted by this gland? 9.3.3 What are the functions of the hormone mentioned in Question 9.3.2? 9.3.4 Which element is essential for the production of the hormone mentioned in Question 9.3.2? 9.3.5 What is meant by basal metabolic rate? 9.3.6 Which disorder/condition is caused by hypothyroidism in:

(a) children? (b) adults?

THERMOREGULATION

QUESTION 10

Answer the following questions about the body temperature of humans. 10.1 What is the normal body temperature (in ºC) of humans? 10.2 Describe the effect of each of the following temperatures on enzyme action: 10.2.1 approximately 60ºC

10.2.2 approximately 4ºC

10.2.3 37ºC 10.3 Why is the maintenance of the temperature in the body fluid seen as such an important aspect of homeostasis? 10.4 What is the main source of heat generation in the human body? 10.5 How does an increase in adrenalin and thyroxin secretions influence heat generation?

10.6 Study the representation below and answer the questions that follow.

10.6.1 List AND explain the four physical processes, numbered 1 to 4 respectively,

of heat loss by the human body. 10.6.2 Name the phenomenon AND describe the role of the blood vessels

numbered 5 and 6 respectively. 10.6.3 Which environmental temperature would probably result in an increase in

metabolic activity, respiration rate and muscle tone, and consequently make

a person shiver?

1

3

4

56

2 (between backpack and body)


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HUMAN REPRODUCTION

QUESTION 1

1.1 ovarian cycle 1.2 1 - Graafian follicle 2 - secondary oocyte

3 - corpus luteum 4 - fimbriae 1.3.1 FSH 1.3.2 oestrogen 1.3.3 LH 1.3.4 progesterone 1.4.1 Fallopian tube 1.4.2 Lined with ciliated epithelium - cilia make sweeping

movements. Smooth involuntary muscles in the uterine walls produce peristaltic movements.

1.5.1 sperm cell 1.5.2 fertilisation 1.5.3 zygote 1.5.4 2 - haploid / (n) / 23 4 - diploid / (2n) / 46

5 - diploid / (2n) / 46 6 - haploid / (n) / 23

7 - diploid / (2n) / 46 1.6.1 morula 1.6.2 mitosis 1.6.3 blastocyst 1.6.4 � The morula continues to divide mitotically and

forms a mass of cells that are arranged around a fluid-filled cavity.

� This hollow sphere is known as the blastocyst,

with an external layer known as the trophoblast, that plays a role in the feeding of the embryo.

� The inner mass of cells develops into the embryo. 1.7.1 endometrium 1.7.2 It developed more blood vessels and glands. 1.7.3 progesterone and oestrogen 1.7.4 implantation 1.7.5 villi 1.7.6 placenta 1.8.1 decreases dramatically 1.8.2 degenerates 1.8.3 continues 1.8.4 starts again 1.9.1 stays high 1.9.2 continues to function 1.9.3 does not continue 1.9.4 stops

QUESTION 2

2.1 day 14 2.2 day 0 - 6 2.3 Stimulates the development of primary follicles to

Graafian follicles in the ovary. 2.4 An increase in the progesterone levels inhibits the

release of FSH so that only one follicle develops at a time.

2.5 The corpus luteum starts to secrete progesterone

that continues to thicken the endometrium. 2.6 no 2.7 � corpus luteum degenerated

� progesterone levels decreased

� FSH levels start to increase

� LH levels decrease

RESPONDING TO THE

ENVIRONMENT: HUMANS

QUESTION 3

3.1 1 - groove/sulcus

2 - skull/cranium

3 - meninges 4 - cerebrum

5 - corpus callosum 6 - cerebellum

7 - foramen magnum 8 - cervical vertebrae

9 - spinal cord 10 - medulla oblongata

11 - hypophysis 12 - hypothalamus

13 - cerebral ventricles filled with cerebrospinal fluid

3.2 1 - It enlarges the total surface area of the brain so

that many neurons can fit into the limited space of the cranium.

5 - � Conducts impulses between the two hemispheres of the cerebrum.

� Forms a bridge for communication between the hemispheres to coordinate processes.

3.3.1 11 3.3.2 5 3.3.3 9

3.3.4 10/12 3.3.5 4 3.3.6 10

3.3.7 6 3.3.8 9

3.4 cerebrospinal fluid 3.5 � between the arachnoid membrane and pia mater

� in the cerebral ventricles

� in the central canal of the medulla oblongata and the spinal cord

3.6 � serves as a shock absorber

� supplies nerve cells with nutrients and O2

� removes waste

� prevents dehydration of nerve cells

� maintains constant pressure around the CNS 3.7 4 and 6

QUESTION 4

4.1 The functional unit of the nervous system. The pathway along which the nerve impulses are carried from a receptor to an effector to bring about a reflex action.

4.2 It is a quick, automatic response of an effector to a

stimulus received by a receptor. 4.3.1 heat of a candle flame 4.3.2 sensory organs in the skin 4.3.3 muscle 4.4.1 These are natural, inborn reflexes that occur

automatically in response to a stimulus, for example coughing, sneezing, blinking or jerking away from a painful stimulus.

4.4.2 These are reflexes learnt through repetition until it

becomes automatic, for example walking, cycling, writing or reading.

4.5 1 - white matter 2 - grey matter

3 - ganglion 4 - cell body

5 - sensory neuron

6 - interneuron

7 - receptor 8 - effector/muscle

9 - mixed nerve

10 - motor neuron/axon

11 - spinal cord 12 - central canal 4.6.1 sensory neuron - the person will not feel that he is

burning and consequently sustain a serious injury.


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4.6.2 motor neuron - the person will feel pain but will be unable to move his finger because the nerve impulse does not reach the effector; the muscle cannot contract and the limb is paralysed.

4.7.1 C - D - A - B 4.7.2 � The heat stimulus (flame) is detected by the

receptors in the skin of the hand and converted into a nerve impulse.

� The nerve impulse is conducted along a sensory

neuron through the dorsal root of the spinal nerve to the grey matter of the spinal cord.

� The sensory neuron is in synaptic contact with the

interneuron in the grey matter of the spinal cord. � The nerve impulse is conducted to the

interneuron, which serves as the reflex centre. � The interneuron is in synaptic contact with the

motor neuron in the grey matter of the spinal cord.

� The nerve impulse is conducted to the motor

neuron. � The nerve impulse exits the spinal cord through

the ventral root of the spinal nerve and is conducted along the axon of the motor neuron to the effector.

� In this case the effector organ is the muscle of the

upper arm, the biceps muscle. � The biceps contracts very quickly, causing the

hand to pull away from the flame. � Nerve impulses are also conducted from the

spinal cord, in ascending nerve tracts, to the brain (cerebrum), where the sensation of pain is interpreted.

QUESTION 5

5.1.1 1, 12 5.1.2 2, 8, 9 5.1.3 3, 4, 6 5.2 1 - sclera 2 - choroid

3 - retina 4 - yellow spot

(fovea centralis)

5 - optic nerve 6 - blind spot

7 - suspensory ligament

8 - ciliary body/muscle

9 - iris 10 - lens

11 - pupil 12 - cornea

13 - eyelid

14 - anterior cavity with aqueous humour

15 - posterior cavity with vitreous humour 5.3.1 Functions:

� protects the internal parts of the eye

� helps to maintain the spherical shape of the eyeball

� serves as a muscle attachment Adaptations:

� strong, inelastic layer of connective tissue 5.3.2 Functions:

� allows light rays through to the inner eye

� causes the refraction of incoming light rays Adaptations:

� transparent

� more convex than the rest of the eyeball 5.3.3 Functions:

� pigment absorbs excess light rays and so prevents internal reflection and the formation of blurry images

� blood vessels supply oxygen and nutrients to cells Adaptations:

� thin

� darkly pigmented

� vascular 5.3.4 Function:

� contracts and relaxes to change the curvature of the lens during eye accommodation

Adaptations:

� consists of involuntary, ciliary muscles

� is attached to the lens by suspensory ligaments

5.3.5 Function:

� changes shape to refract light rays coming from near and far objects to form a clear image on the retina

Adaptations:

� elastic

� transparent

� biconvex

� able to change shape 5.3.6 Function:

� controls the amount of light that enters the eye by controlling the size of the pupil

Adaptations:

� a round, coloured structure suspended towards the centre of the eye like a circular curtain

� situated in front of the lens � has two sets of involuntary muscles, the radial

and circular muscles � has an opening in the middle, the pupil, through

which light rays enter the eye � contains pigments that give colour to the eye and

absorbs light rays 5.3.7 Function:

� absorbs light rays and prevents internal reflection Adaptation:

� darkly pigmented 5.3.8 Function:

� detects light stimuli and converts it to nerve impulses

Adaptation:

� contains two types of photoreceptors, i.e. rods and cones

5.3.9 Function:

� conducts nerve impulses to the cerebral cortex of the brain where they are interpreted and the sensation of sight originates.

Adaptation:

� nerve fibres from the photoreceptors form a synapse with sensory bipolar neurons, which in turn form a synapse with optic neurons. The optic neurons join together to form the optic nerve.


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5.3.10 Functions:

� helps to keep the shape of the eyeball. � keeps the retina in position against the choroid. � refracts the light rays to form a sharp image. Adaptations:

� jelly-like � transparent 5.4.1 The yellow spot is an area on the retina, in the

direct line of vision which contains mainly cones and very few rods. In the middle of the yellow spot is the fovea centralis which contains cones only. The brightest, most accurate image is formed here.

The blind spot is the place where the optical nerve

leaves the eyeball and no rods or cones occur. If light rays were to fall on the blind spot, no nerve impulses will be conducted to the brain and no images will form.

5.4.2 The aqueous humour is a watery fluid that fills the

anterior cavity, situated between the lens and the cornea. It helps the cornea to keep its shape, supplies nutrients to the eye and protects the eye from pathogens.

The vitreous humour is a jelly-like fluid that fills the

posterior cavity, situated behind the lens. It helps to maintain the shape of the eyeball, prevents the retina from detaching from the choroid and helps with light refraction.

5.5.1 retina 5.5.2 photoreceptors 5.5.3 detect light stimuli and convert them to

nerve impulses 5.5.4 (a) react when the light intensity is low (poor light)

and give rise to black and white vision (b) react when the light intensity is high (daylight)

and give rise to intense, bright, colour vision 5.5.5 (a) fovea centralis of yellow spot (b) blind spot (c) fovea centralis of yellow spot

QUESTION 6

6.1 accommodation 6.2 The process during which the eye adapts for the

observation of nearby or distant objects by changing the shape of the lens.

6.3.1 B 6.3.2 A 6.4.1 1 - ciliary muscles 2 - suspensory ligament

3 - lens 6.4.2 For nearby objects (closer than 6 m), the curvature

of the lens has to change to focus the incoming light rays on the retina. The following changes take place during eye accommodation:

� ciliary muscles (circular muscles) contract

� ciliary body moves closer to the lens

� the suspensory ligaments slacken (less tension)

� elastic lens becomes more convex

� more refraction of light rays by the thicker lens

� a sharply focused image falls on the retina 6.5 The lens loses its elasticity after the age of forty.

Consequently, the lens can no longer change its curvature effectively. Light rays from nearby objects can no longer be refracted enough to form a sharp, focused image on the retina. Therefore, the light rays need to be refracted by the convex lenses of glasses to provide a focused image on the retina.

6.6.1 D - the learner’s book is closer than 6 m from the

eye and therefore the lens needs to accommodate and become more convex, maintaining that shape until all the homework has been checked

6.6.2 C - the lens needs to adapt to the cricket ball

moving closer to the eye; the lens is unaccommodated when the ball is far away, but as it moves closer, it becomes more and more convex

6.6.3 A - the lens does not have to adapt, because the

stage is probably more than 6 m away from the person sitting still and watching the violinist; the lens remains flat as the distance remains constant

6.6.4 B - the lens is more convex to focus on the child on the tricycle, who is closer than 6 m from his mother, but as the toddler travels down the road, the lens becomes flatter and returns to the unaccommodated state

QUESTION 7

7.1 A - outer ear B - middle ear

C - inner ear 7.2 mechanoreceptors 7.3 1 - pinna - collects and directs sound waves

towards the external auditory opening 2 - external auditory canal - transmits sound waves

from the pinna to the tympanic membrane 7.4 3 - hammer (malleus) 4 - anvil (incus)

5 - stirrup (stapes) 7.5 They amplify and transmit vibrations to the

membrane of the oval window. 7.6 6 - tympanic membrane/eardrum - converts sound

waves to vibrations that are transmitted to the hammer

7 - oval window - transmits vibrations from the air-filled middle ear to the fluid-filled inner ear (perilymph)

8 - round window - absorbs the pressure waves from the perilymph of the scala tympani

7.7 Eustachian tube - ensures that the pressure remains

the same on both sides of the tympanic membrane. 7.8.1 9 - semicircular canals

10 - vestibular apparatus/sacculus and utriculus 7.8.2 cristae - detect changes in the speed and

movement of the head 7.8.3 sacculus, utriculus 7.8.4 maculae - respond to gravity and detect the

position of the head in space 7.9.1 11 - cochlea 7.9.2 organ of Corti


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7.10.1 12 - vestibular nerve

13 - cochlear nerve 7.10.2 14 - auditory nerve - conducts nerve impulses to the cerebral

cortex where the sensation of hearing arises - conducts nerve impulses to the cerebellum

where balance is coordinated

QUESTION 8

8.1 A - sacculus B - utriculus 8.2 1 - ampulla 8.3.1 cristae 8.3.2 The cristae occur in the ampullae of the semicircular

canals. A crista consists of sensitive hair cells imbedded in a jelly-like cap, the cupula. Nerve fibres, forming part of the vestibular nerve, conduct nerve impulses from the cristae to the cerebellum.

8.3.3 Cristae detect changes in the speed or movement of

the head. 8.3.4 As soon as the head turns in a particular direction,

the endolymph in the corresponding canal will move. The moving endolymph displaces the cupula of the cristae and causes it to move. The moving cupula bends the sensory hair cells. These mechanical stimuli are converted into nerve impulses by the bent hair cells. The nerve impulses are conducted by nerve fibres forming part of the vestibular nerve, from the cristae to the cerebellum of the brain, where balance is coordinated.

8.4.1 macula 8.4.2 Inside the utriculus and sacculus are areas with hair

cells embedded in a jelly-like layer. There are

calcium carbonate (CaCO3) crystals, called otoliths in the jelly. The hair cells, jelly-like layer and otoliths, form a receptor called a macula. Nerve fibres, that are part of the vestibular nerve, conduct nerve impulses from the maculae to the cerebellum.

8.4.3 The maculae respond to gravity and detect the

position of the head in space.

8.4.4 The otoliths (CaCO3-crystals) in the jelly-like layer of the maculae move in response to gravity. When the position of the head changes, the otoliths exert more pressure on some hair cells than others. The hair cells convert mechanical stimuli into nerve impulses.

HUMAN ENDOCRINE

SYSTEM

QUESTION 9

9.1 1 - hypophysis/pituitary gland 2 - thyroid

3 - adrenal glands

4 - pancreas/islets of Langerhans

5 - ovary 6 - testis 9.2.1 The hypophysis is located at the base of the brain,

attached to the hypothalamus by a short stalk. It fits into a small bony cavity in the cranium.

9.2.2 hypothalamus 9.2.3 � The hypothalamus is connected to the

hypophysis in two ways: - by blood vessels to the anterior lobe - by neurons to the posterior lobe � The hypothalamus produces hormones (e.g.

ADH) which are transported via the neurons to the posterior lobe of the hypophysis for storage.

� The hypothalamus controls the hypophysis by

secreting releasing factors via the neurons (to the posterior lobe) or via the blood (to the anterior lobe). The releasing factors stimulate the hypophysis to produce and/or release hormones into the blood.

9.2.4

Hormone Function

TSH (thyroid stimulating hormone)

stimulates the thyroid to secrete the hormone thyroxin

Growth hormone (STH/somatotropic hormone)

promotes the growth of the skeleton and muscles by stimulating the synthesis of proteins

FSH (follicle stimulating hormone)

stimulates the development of primary follicles into Graafian follicles in the ovary of the female, and it activates the germinal epithelial cells that produce sperm in the male.

LH (luteinising hormone)

stimulates ovulation (release of the egg cell) and the development of the corpus luteum in the ovary of the female

Prolactin stimulates the mammary glands to produce milk after the birth of a baby

9.2.5 (a) dwarfism

(b) giantism

(c) acromegaly 9.2.6 ADH (antidiuretic hormone) - ADH controls the

reabsorption of water by making the walls of the renal tubules and collecting ducts more permeable to water. More water is reabsorbed from the filtrate and less water excreted with the urine. Therefore, ADH helps to conserve water in the body.

9.3.1 It is located on either side of the trachea, just

below the larynx. 9.3.2 thyroxin 9.3.3 � It increases the basal metabolic rate. � It increases the breathing rate and heart rate. � It is essential for normal growth and development

of organs. � It is essential for normal functioning of the

nervous system 9.3.4 iodine 9.3.5 It is the amount of energy the body needs to

function when it is at rest. 9.3.6 (a) cretinism (b) myxoedema

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THERMOREGULATION

QUESTION 10

10.1 37ºC 10.2.1 The enzyme(s) will denature. They will therefore

lose their shape permanently and cannot fulfil their vital function, meaning that enzyme action stops permanently.

10.2.2 The enzyme(s) will be temporarily inactive or

enzyme action will be very slow. If optimum temperature is reached once more, they will function at maximum capacity.

10.2.3 The enzyme(s) will be able to function optimally so

enzyme action will therefore be at a maximum. 10.3 Enzymes are biological catalysts that control and

regulate all bodily functions. It is thus necessary that body temperature is kept constant for the optimal functioning of enzymes.

10.4 cellular respiration 10.5 It leads to an increased metabolic rate, resulting in

an increased respiratory rate and release of heat. 10.6.1 1 - Radiation

- It is the loss of heat energy from a warm body to a cold environment by means of rays or waves.

2 - Conduction

- It is the transfer of heat energy from warm to cold objects in contact with each other.

3 - Evaporation

- Occurs when a fluid absorbs heat energy and changes into a gas. When sweat evaporates from the surface of the body, heat energy is released from the body and the body cools.

4 - Convection

- It is the distribution of heat in fluids or gases. Air in direct contact with the body is warmed by body heat and rises. Cold air replaces the warm air.

10.6.2 5 - Vasodilation

- More blood flows to the skin surface, resulting in more heat loss through radiation, convection or conduction. More blood also flows to the sweat glands, resulting in increased sweat secretion. More sweat evaporates from the skin surface leading to increased heat loss.

6 - Vasoconstriction

- Blood is redirected to blood vessels in the deeper skin layers. Less blood flows to the skin surface with the result that less heat is lost through radiation, convection or conduction. Less blood also flows to the sweat glands, resulting in decreased sweat production. Less sweat evaporates from the skin surface and therefore heat loss is reduced.

10.6.3 decreased/low environmental temperature







gr 12 life sciences: paper 1 - the...

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