AS Human Biology Unit 10

Text questions

P178/Q1		Transcription
P178/Q2		Cell division in: (a) fertilised egg (→morula → blastocyst → embryo → �) (b) epithelium of the intestines (c) epidermis of the skin
P180/Q3		46 chromosomes
P180/Q4		Nuclear envelope & nucleus disappeared. Chromosomes formed from chromatin.
P180/Q5		Spindle fibres are not on the same plane/some of the fibres are higher, some of them are lower.
P181/Q6	a)	Long & thin chromosomes = DNA only partly coiled up (: replication/transcription possible).
	b)	Chromosomes short & fat = separation of sister chromatids & their movement to the opposite poles of the parent cell possible.
P182/Q7		Prophase: C Metaphase: B Anaphase: A Telophase: D
P182/Q8		G1, S, G2

Assignment

P185/Q1	a)	Animal cells: no cell wall, spindle apparatus attached to centrioles.
	b)	Anaphase: sister chromatids separated & moving to the opposite cell poles.
P185/Q2	a)	8mm
	b)	8mm = 8000 micrometers (μm) 8000 μm / 250 = 32μm
P185/Q3		Nuclei C: 14 chromosomes and 5 units of DNA each.
P186/Q4	a)	No, because RBC have no nuclei.
	b)	Yes, because epithelial cells have nuclei; they must divide to replace the worn out cells.
	c)	No, because they are dead/keratinised.
P186/Q5	a)	Try it yourself
	b)	Try it yourself
P186/Q6	a)	Prophase. Many events/processed take place during this phase: Coiling up of DNA → formation of chromosomes; Nuclear envelope & nucleolus disappear; Movement of centrioles to the poles of the cell; Early stages of formation of spindle apparatus.
	b)	Compare this question with the Exam question 2b(II), page 187, and try to answer it yourself.

Examinations

P187/Q1

(i) Interphase (S)

(ii) Anaphase

(i) D

(ii) Aceto - orcein

(iii) Stain is taken up by chromosomes, making them (more) visible

P188/Q2

(i) Prophase

(ii) Interphase (S)

(i) Aceto - orcein

(ii) Table 10.4, p.187

Stage of cell cycle	Number of cells seen	% time in cell
Interphase	147	60
Prophase	68	28
Metaphase	10	4
Anaphase	4	2
Telophase	15	6
TOTAL	244	100

P188/Q3

DNA is the genetical material, which codes for proteins. Structure of DNA codes for/is linked with the structure of proteins, hence more DNA → more proteins.

(i) Live capsulated (→ when injected into mice → mice died of pneumonia).

(ii) (Some research may be needed to answer this question). DNA from dead capsulated bacteria is incorporated into the DNA of live non-capsulated bacteria. This "virulent" DNA codes for toxins which cause infection in mice.

(i) Radioactive phosphorus used to label DNA;

(ii) Genetic material = DNA.