SECTION C SAMPLE ANSWERS

Question 1

Outline the transport of lipids from small intestines to where they are stored

Answer 1

• absorbed into lacteal of villi in the ileum of the small intestine by diffusion
• transported into lymphatic system (as lipids cannot spend a large amount of time in circulatory system)
• enter the circulatory system at sub-clavian vein in neck
• transported to the liver to be stored via hepatic portal vein

Question 2

How does the anther produce pollen? / explain the formation of the pollen grains from the microspore mother cell

Answer 2

Total of 4 pollen grains produced by each anther. A diploid microspore mother cell (2n) found in the anther of the stamen divides by meiosis to produce 4 haploid cells (n). The nucleus of each haploid cell (pollen) divides by mitosis to produce a generative nucleus and a tube nucleus. A total of 4 pollen grains are produced which ae then released from the anther when it loses water, shrivels up and spits open causing the anther to burst and release the pollen grains to be transferred to the female reproductive organ through a process known as pollination.

Question 3

Explain the formation of the female gametes from the megaspore mother cell

Answer 3

• Diploid (2n) megaspore mother cell located in embryo sac.
• Divides by meiosis to produce 4 haploid (n) daughter cells.
• 3 of these daughter cells die.
• Surviving daughter cell undergoes a series of mitosis 3 times to produce 8 haploid (n) cells.
• 5 disappear / disintegrate.
• The remaining 3 (all haploid) divide into two groups.
1. 2 haploid cells group together to give polar nuclei (n) + (n) = 2n
2. 1 haploid cell becomes known as egg cell (n).

Question 4

outline the events involved from the pollen grain landing on the stigma up to and including fertilisation

Answer 4

fertilisation in plants - double fertilisation.

1. pollen grain lands on style and releases both nuclei (tube and generative).
2. A pollen tube is created down through stigma, style and ovary to allow the pollen grain to travel to female gametes. This pollen tube is formed by the tube nucleus of the pollen grain with the assistance of enzymes. Once the pollen tube has formed all the way to the embryo sac the tube nucleus disintegrates.
3. As the generative nucleus travels down style it undergoes mitosis to produce 2 identical haploid gametes (n).
4. Both pollen gametes travel into the ovule via the micropyle where there are 2 female gametes present (egg & polar nuclei).
5. One pollen gamete fuses with the egg to produce a diploid zygote - single cell which undergoes mitosis to produce multicellular embryo. Embryo consists of plumule and radicle. Plumule will become future shoot when the plant germinates, and the radicle will become the future root.
6. The other pollen gamete fuses with the polar nuclei to produce a triploid endosperm (3n) which will act as a food source for the developing seed while it is in a period of dormancy.
7. Steps 5 & 6 = double fertilisation
8. A seed will develop from ovule - the coat of the seed (testa) develops from the integument (lining of ovule).
9. Fruit will develop from ovary.

Question 5

explain the role of the pacemaker in a heart beat

Answer 5

• Blood enters both atria of the heart via vena cava and pulmonary vein.
• When the atria are full, atria contract (systole) due to the SA node of the pacemaker (located in the upper walls of the right atrium), emitting an electrical impulse in the form of ions and tricuspid / bicuspid valve open blood passes into ventricles.
• Valves close to create a “lub” sound
• Atria muscles relax (diastole).
• When ventricle chambers are full, ventricles contract (systole) due to AV node of the pacemaker (located in the lower walls of the right atrium), emitting an electrical impulse and force blood out of heart to either lungs or around the body via semi lunar valves.
• Once blood has left heart, semi-lunar valves close creating a “dub” sound and ventricle muscles relax (diastole)
• This cycle takes 0.8 seconds
• The number of times this cycle occurs in a minute is measured by pulse.
• The average number of heart beats is 68bpm
• Heartbeat is an involuntary cardiac muscle located in the thoracic cavity that never fatigues.

Question 6

mechanism to transport message across synaptic cleft

Answer 6

1. Electrical impulse carried along axon of the pre synaptic neuron in the form of ions.
2. Reaches axon terminal
3. Synaptic swellings produce neurotransmitter that is released into synaptic cleft. examples of neurotransmitters = dopamine, nor-adrenaline, acetyl choline.
4. Electrical impulse now chemically carried across cleft ad picked up by dendrite of next neuron
5. Neurotransmitter broken down by enzymes and reabsorbed into pre synaptic cleft.

Question 7

mechanism of a reflex action

Answer 7

• Electrical messages carried to spinal cord via sensory neuron
• Enters spinal cord via dorsal root ganglion
• Converted into a motor neuron via the interneuron located inside the spinal cord. Message passed out of spinal cord on the motor neuron via ventral root
• Message carried to muscle where reaction occurs.

Question 8

Explain the events involved in the inhalation of air

Answer 8

• High CO2 levels in blood detected by medulla oblongata
• Sends an electrical impulse from brain to lungs
• Diaphragm contracts and flattens
• Intercostal muscles contract
• Ribcage moves up and out
• Volume of lungs increases
• Pressure inside lungs is lower that external surroundings
• Air is taken in from the surrounding environment.

Question 9

Sexual reproduction in the rhizopus

Answer 9

• Location: between 2 hyphae of different Rhizopus
• Hyphae of opposite Rhizopus join
• Swelling occurs at point of joining. Known as progametangium
• Gametes moves into progametangium. Swelling of each hyphae containing gametes now known as gametangium.
• Wall of gametangium break down and gametes fuse to form zygote (baby Rhizopus)
• Develops into a zygospore (zygote with a protective layer around it)
• If conditions are favourable: zygospore reproduces to form new Rhizopus
• If conditions are not favourable: zygospore remains dormant.

Question 10

asexual reproduction in rhizopus

Answer 10

• Location: sporangium
• Occurs 2-3 days after incubation period
• Spores inside sporangium divides many times by mitosis
• Sporangium dehydrates and bursts
• Spores released and dispersed by wind
• If conditions are favourable, spores germinate to form new Rhizopus
• This method of asexual reproduction is known as sporulation

Question 11

asexual reproduction of yeast

Answer 11

• Asexually by budding
• The parent cells form an outgrowth or bud that fills with cytoplasm
• The nucleus divides by mitosis
• One nucleus moves into the bud
• The bud is cut off from the parent cell forming a new genetically identical daughter cell
• Rapid budding produces a small group (colony) of attached cells

Question 12

transpiration stream

Answer 12

Water molecules move across the ground tissue into the vascular tissue by diffusion
• Water needs to travel up the vascular tissue against the force of gravity
• The water absorbed by the root will travel up the first 1 ½ metre due to root pressure
• Water molecules travel up the stem due to the adhesion/cohesion tension model – the attraction the water molecules have with eachother and the walls of the xylem. Water molecules are pulled up the xylem until they reach the stomata to leave the leaf where is split by photolysis during photosynthesis. Any excess water cannot be stored in the vacuoles is released into atmosphere via stomata. (transpiration).
• The xylem vessels aid transport of water by lying end to end, having narrow tubes and the presence of pits
• Discovered by joly and Dickson.

Question 13

illustrate specificity of enzymes

Answer 13

• Enzyme joins with substrate. The shape of the enzyme allows it to fit with only one substrate i.e. enzymes are specific. Reaction occurs at active site.
• Forms enzyme substrate complex
• Enzyme changes shape of substrate to form product
• Product and enzyme released, enzyme remains same shape and therefore can be reused
• This is known as the active site theory / induced fit model.

Question 14

outline the response of a plant to a names external stimuli

the effect of tropism light on the internal production of the growth regulator IAA

Answer 14

• When the amount of light is low (i.e. shaded part of plant structure) IAA production is greater as a result of greater cell elongation
• When the amount of light is high (i.e. part of the plant the sun is shining on) IAA production is lower
• This causes the plant structure to bend due to the difference in the amount of IAA and the greater amount of IAA causes the plant to bend towards the light-positively phototrophic.

Question 15

bone formation

Answer 15

• Starts as a cartilage
• Changes to bone due to the presence of osteoblasts cells (which produce protein and collagen)
• Hardens due to calcium, protein part of bone remains flexible.

Question 16

lengthening of bone (in teenagers)

Answer 16

• Occurs in growth plates of bone. Growth plates made of cartilage and found between shaft and head of bone
• Growth plates produce cartilage (cartilage stimulated by hormone produced in the pituitary gland)
• Cartilage changes to bone
• Growth plate changes to bone in adults and stops bone growth

Question 17

bone renewal (bones stop growing in adults but still need to be renewed)

Answer 17

• Vitamin D and calcium required for this
• Osteoclast cells digest old bone into the medullary cavity and release calcium into the blood for the formation of new bone
• Amount of renewal depends on:
o Physical activity
o Diet
o hormones

Question 18

outline the events involved in viral replication

Answer 18

• Virus attaches itself to the surface of the host cell
• Virus pierces a hole in the membrane of the host cell
• DNA/RNA enter host cell
• Protein coat remains outside
• DNA/RNA replicate inside the host cell multiple times asexually
• Host cell bursts and releases the replicated viruses which then go on to repeat the process again

Question 19

explain the events involved in bacterial reproduction

Answer 19

Unicellular: single celled organisms that reproduces by binary fission (mitosis / asexual reproduction)
• DNA replicates
• Cells elongate and grow
• Membrane forms around replicated information and cells divide
• Results in two identical daughter cells produced
• Happens every 20 minutes
• Rapid reproduction rate results in mutations and can lead to resistance to antibiotics

Question 20

explain how the human body responds as a result of a warm day, vigorous exercise and salty food consumption

Answer 20

• Water level in the blood is low detected by the hypothalamus in the brain sends a message to the pituitary gland in the brain to produce a large amount of ADH.
• Travels in the blood to the distal convoluted tubule / collecting duct of the nephron in the blood
• ADH increases the permeability of the nephron wall
• Large volume of water is reabsorbed by the nephron back into the blood
• Volume of urine is low
• Has a high salt concentration
• Dark yellow / brown in appearance

Question 21

outline the response of the human body to an antigen that manages to avoid the 1st and 2nd lines of defence

Answer 21

• Helper t-cells detect antigen and send message to b-cells to produce antibodies that surround antigen
• Killer t-cells secrete perforin which poisons and kills the antigen
• Antigen now dead and suppressor t-cells will stop production of perforin so not to damage “healthy” cells
• Dead antigen / antibody complex engulfed by phagocyte

Question 22

explain the development of the baby following fertilisation

Answer 22

• Diploid zygote formed following fertilisation
• Undergoes mitosis to form a solid ball of cells called a morula. This happens in fallopian tube
• Morula embeds itself into endometrium
• Morula divides into trophoblast and blastocyst
• Trophoblast will develop into the placenta of the baby. The role of the placenta is to exchange materials between mother and baby during pregnancy by diffusion
• Baby will develop from blastocyst by dividing into 3 germ layers
• A germ layer is defined as being a single layer of cells
• These 3 germ layers are ectoderm, mesoderm and endoderm
• Skin will develop from ectoderm
• Muscle tissue will develop from mesoderm
• Linings such as pleural membrane around lungs will develop from endoderm
• Baby will be surrounded by amnion (fluid filled amniotic sac) that will protect the baby by acting as a shock absorber

Question 23

explain a feedback mechanism with regard to hormones making refernece to a specific example

Answer 23

• A feedback mechanism involves the quantity of a hormone controlling the production of itself or the production of another hormone
• There are two types of feedback: negative and positive
• Positive feedback mechanism: the production of one hormone increases the production of a second hormone by a glad (eg high levels of TSH increase the production of thyroxine by the thyroid)
• Negative feedback mechanism: the production of the second hormone (thyroxine) results in a decrease of the first hormone (TSH) by a gland (pituitary). (eg high levels of thyroxine now cause a decrease in TSH in the pituitary)
• Example: TSH and the thyroid. Thyroid stimulating hormone (TSH – produced in the pituitary gland) controls the quantity of thyroxine produced by the thyroid. High levels of TSH send a message in the blood to the thyroid to increase the production of thyroxine. This is the positive feedback mechanism. As a result of this high level of thyroxine this sends a message back to the pituitary to stop the production of TSH. This is known as a negative feedback mechanism