Answers to Hands on Pg 50

Section B
3a) Meiosis is a process of cell division producing gametes which are haploid (n) as compared to the parent cell which is diploid (2n).
b)

A chromosome consists of 2 chromatids held together at the centromere.

Paring of homologous chromosomes occurs

Crossing over takes place.

Nuclear membrane and nucleolus disappear.

c)

MITOSIS	MEIOSIS
Takes place in somatic cells	Takes place in reproductive cells
Produce new cells for growth or tissue repair.	Produce gametes
Involves one division only in one cycle	Involves two divisions in one cycle
No pairing of homologous chromosomes	Pairing of homologous chromosomes during Prophase I
Crossing over does not occur	Crossing over occurs during Prophase I
2 diploid cells are produced	4 haploid cells are produced
The number of chromosomes in a daughter cell is the same as its parent cell	The number of chromosomes in a daughter cell is the halvedof its parent cell
The daughter cells are identical to the parent cell	The daughter cells are not identical to the parent cell and to each other

4a) Process of cell division is mitosis.

Preparatory stage is interphase.

Interphase

· Replication of DNA

· Storage of energy

· More organelles are produced

· Mitosis consist of prophase, metaphase, anaphase and telophase

Prophase

· Chromosomes thicken and shortens

· Each chromosomes consists of 2 chromatids

· Nuclear membrane and nucleolus starts to disappear

Metaphase

· Chromosomes are arranged in a line across the middle of the cell

· Centrosomes are held by spindle fibre

Anaphase

· Centromeres of chromosomes divide into 2.
· Chromatids are separated and pulled to the opposite poles of the cell.

Telophase

· Spindle fibres disappear

· Nuclear membrane reappear

· Chromosomes are seen as fine threads

. Formation of cell plates begin

b) Tissue culture can be used to produce more seedlings.

Small pieces of meristem tissue/explant are removed from a parent plant and cut it into small pieces.
Sterilise the pieces of tissues with dilute sodium hypochlorite solution.
Place each sterile tissue onto a culture medium containing nutrients and growth hormone.
The tissue cells are left to divide by mitosis to produce a mass of loosely arranged and undifferentiated cells called callus.
The callus is then stimulated with shoot stimulating hormones to form multiple shoots.
Separate the shoots in nutrient medium with root stimulating hormones to encourage rooting.
Once the roots grow, the plantlets (little plants) are planted in sterile soil to grow into adult plants.

Cloned banana plant

Discuss how you can produce a cloned banana plant.
Suggested answer
Small pieces of meristem tissue/explant are removed from a parent banana plant and cut it into small pieces.
Sterilise the pieces of tissues with dilute sodium hypochlorite solution.
Place each sterile tissue onto a culture medium containing nutrients and growth hormone.
The tissue cells are left to divide by mitosis to produce a mass of loosely arranged and undifferentiated cells called callus.
The callus is then stimulated with shoot stimulating hormones to form multiple shoots.
Separate the shoots in nutrient medium with root stimulating hormones to encourage rooting.
Once the roots grow, the plantlets (little plants) are planted in sterile soil to grow into adult plants.

To determine the energy value in food samples.

Objective	To determine the energy value in food samples.
Problem statement	What is the energy value in cashew nut and groundnuts?
Hypothesis	Cashews nuts have higher energy value than ground nuts.
Variables	Manipulated : Types of food sample: Cashew nut and ground nut
	Responding : The rise in temperature of water//Energy value
	Constant : Volume of distilled water
Apparatus and materials	Apparatus (A): Boiling tubes, retort stand, plasticine, long pins, thermometer, electronic weighing scale, 25ml measuring cylinder Materials (M) :Fresh ground nuts, fresh cashews nuts, distilled water and matches
Technique	Measure and record the rise in temperature by using a thermometer// Calculate the energy value using the formula: Energy value = 4.2 (Jg-1 oC-1) x mass of water (g) x increase in temperature(oC)/Mass of peanut(g)
Procedure	Weigh the cashew nut and record its weight. Fill a boiling tube with 20ml of distilled water. Clamped the boiling tube to a retort stand. Record the initial temperature of the distilled water. The pointed end of a long pin is poked into the cashew nut. The other end of the pin is poked into with a piece of plasticine. The cashew nut is ignited by using a match stick and immediately placed under the boiling tube. The flame from the cashew nut is allowed to heat up the water. The water is stirred gently by using a thermometer to distribute the heat evenly. At the same time the rise in temperature is observed. Measure and record the final temperature using the thermometer. Record the final temperature of the water in a table. The energy value of the cashew nut is calculated using the formula : Energy value = 4.2 (Jg-1 oC-1) x mass of water (g) x increase in temperature (oC)/ Mass of peanut(g) 10. Steps 1 to 9 are repeated by using a groundnut. 11. Precaution : a) Make sure that the nut is fully burnt. b) A shield is put around the nut to prevent heat loss to the surrounding.
Recording data/ result	Food sample Cashew nut Groundnut Weight(g) Initial temperature of water (oC) Final temperature of water (oC) Rise in temperature (oC) Energy value (J)
Conclusion	Cashew nut has a higher energy value than groundnut. The hypothesis is accepted.

Answers to Hands on Pg 49-50

1. a)b) The daughter cell is identical to the parent cell.
c) i) It produces new cells for growth
ii) It produces new cells to replace old or dead tissues.
d) i) Presence of centrioles in an animal cell but none in plant cell.
ii) During cytokinesis, constriction of plasma membrane in an animal cell but formation of cell plate in a plant cell.
e) i) To produce more cell for growth
ii) To produce more seedlings through cloning/tissue culture.

2. a)b) Crossing over takes place at X. During this process, transferring of genes between 2 homologous chromosomes take place. This produces a new combination of genes which bring about variations.
c) Male and female gametes which are produced through meiosis have haploid number of chromosomes (n). When a male gamete (n) fuses with a female gamete (n) during fertilisation, a zygote (2n) is formed. Hence, the diploid condition is restored.
d) i) In anaphase I, the chromosomes separate but in anaphase II, the chromatids separate.
ii) Crossing over takes place in prophase I but there is no crossing over in prophase II.
iii) There is formation of bivalent during prophase I but none in prophase II.