BIOLOGY PAPER 2 - 2019 KCSE CEKENA MOCK EXAMINATION (QUESTIONS AND ANSWERS)

INSTRUCTIONS TO CANDIDATES:

This paper consists of TWO sections A and B.
Answer all questions in section A in the spaces provided.
In section B, answer question 6 (compulsory) and either question 7 or 8 in the spaces provided.

SECTION A (40 MARKS)
Answer all questions in this section in the spaces provided.

The diagram below represents part of phloem tissue.
1. Name the structures labeled R and S and the cell labeled T (3mks)
  R:
  S:
  Cell labeled T:
2. State the function of the structure labeled S. (1mk)
3. Explain why xylem is a mechanical tissue. (2mks)
4. 1. State the effect of removal of the cell labeled T. (1mk)
  2. Give a reason for your answer in (a) above. (1mk)

1. Describe the following chromosomal mutations:
  1. Inversion (2mks)
  2. Translocation (2mks)
2. In mice the allele for black fur is dominant to the allele for brown fur. What percentage of offspring would have brown fur from a cross between 2 heterozygous black mice? Show working. Use letter B to represent the allele for black colour.(4mks)

Study the diagram below and answer the questions that follow.
1. 1. Which part marked a, b, c and d, when defective after implantation may lead to abortion (1mk)
  2. Give a reason for your answer. (1mk)
2. The part labeled b can be removed after 4 months of pregnancy without interfering with the pregnancy. Explain. (2mks)
3. Under each of the following, state the name of the causative agent.
  1. Syphillis (1mk)
  2. Gonorrhea (1mk)
  3. AIDS
4. State two disadvantages of external fertilization. (2mks)

Study the figure below and answer the questions that follow.
1. Which solution has higher concentration of free water molecules? (1mk)
2. Which solution is more concentrated? (1mk)
3. In which direction will osmosis take place? Indicate using an arrow on the diagram. (1mk)
4. What does semi-permeable membrane represent in an animal cell (1mk)
5. 1. Define the term active transport (1mk)
  2. Why is oxygen important in active transport in cells (2mks)
6. When red blood cells are placed in a hypotonic solution they burst.Name the process involved.(1mk)

The flow diagram below represents passage of a meal through the human digestive system. Study the diagram and answer the questions that follow.
1. Name the physical process that will occur in mouth cavity (1mk)
2. Name the digestive juices B and C (2mks)
3. Explain two ways in which the digestive system is protected from corrosive effects of digestive juices. (2mks)
4. Name the hormone that stimulates secretion of juice B. (1mk)
5. Identify two contents of digestive juice A (2mks)

SECTION B – 40 MARKS
Answer question 6 (Compulsory) and any other one question from this section.

During germination and growth of a cereal, the dry weight of endosperm, the embryo and total dry weight were determined at two-day intervals. The results are shown in the table below.
1. Using the same axes, draw graphs of dry weight of endosperm, embryo and the total dry weight against time. (8mks)
2. What is the total dry weight on day 5? (1mk)
3. Account for:
  1. Decrease in dry weight for endosperm from day 0 to 10. (2mks)
  2. Increase in dry weight of embryo from day 0 to 10. (2mks)
  3. Decrease in total dry weight from day 0 to day 8. (2mks)
  4. Increase in total dry weight after day 8. (1mk)
4. State one cause of dormancy: (2mks)
  1. Within a seed
  2. Outside the seed
5. State two ways of breaking seed dormancy (2mks)

Explain the role of human skin in:
1. Thermo regulation. (14mks)
2. Protection (6mks)

Explain various ways in which fruits and seeds are adapted to dispersal. (20mks)

MARKING SCHEME

1. R - Sieve pore;
  S – Cytoplasmic strands / filaments;
  Cell T – companion cell;
2. Translocation;
3. They are thickened; and lignified;
4. 1. Active transport will not occur;
  2. Reason: Because of lack of energy;

1. 1. Inversion
    Occurs when chromatids break at two places; and when rejoining the middle piece rotates and joins in an inverted position;
  2. Translocation
  3. Occurs when a section of chromatid breaks off; and becomes attached to another chromatid of another chromosome;
2. Parents ♂                          ♀
  Parental phenotype                        Black fur                    Black fur
  Parental genotype              Bb                   x          Bb
  
  *Penalise at parental genotype if other letters are used.
  *Maximum of 1 mark if wrong symbols used for correct crossing.

1. 1. C;
  2. It is the uterine wall where implantation occurs;
2. Part b secretes the hormones oestrogen and progesterone before 4 months of pregnancy; This role is taken over by placenta hence no active role; progesterone and oestrogen maintain pregnancy.
3. 1. Treponema pallidum names that are not underlined (i & ii)
    - other rules spelling of binomial nomenclature
  2. Neisseria gonorrhoea
  3. Human immune deficiency virus rej. HIV
4. gametes are less protected Low chances of fertilization; high rate of predators attacking eggs

1. Solution A;
2. Solution B;
3. Arrow from A Pointing B;
4. Cell membrane / Plasma membrane;
5. 1. Movement of ions/molecules from where they are lowly concentrated to where they are highly/against conc.gradient by use of energy.
  2. Oxygen is required in respiration to generate energy/ATP
6. Haemolysis
1. Mastication;/chewing;/grinding; any one (1mk)
2. B – Gastric juice; (1mk)
  C – Intestinal juice;/ succus entericus; (1mk)
  reject wrong spelling
3. Has Goblet cells that secret mucus: mucus forms a protective barrier
  - Enzymes produced in inactive form that is pepsinogen and trypsinogen (2mks)
4. Gastrin; (1mk)
5. – Enzyme salivary amylase.Ptyalin;
  - Mucin/Mucus;
  - Water; (any two) (2mks)
2. 5,g Acc + 0.5;
3. 1. Hydrolysis of starch into simple sugars; which are transported to the embryo;(Respiration to give energy). Accept simple sugars oxidized rej. oxidation of starch.
  2. New materials are synthesized from protein; bringing about growth of embryo;
  3. The rate of respiration is faster; than that of synthesis of materials for growth;
  4. Foliage leaf carried out photosynthesis leading to growth;
4. 1. - Presence of absiscic acid / Germination inhibitors;]
    - Embryo not fully developed;
    - Absence of hormones / enzymes to stimulate germination;
    - Impermeable seed coat; rej. hard seed coat. (any one)
  2. - Unsuitable / unfavourable temperature;
    - Absence of light;
    - Lack of water;
    - Lack of oxygen; (any one)
5. scarification
  - Allow embryo to mature
  - Increase in conc.of hormones eg cytokinins n gibberellins that stimulate germination
  - Favourable environmental factors eg water 0xygen and suitable temperature
  - Suitable wavelength of light that trigger production of hormones like gibberellins.
1. When the temperature is low (cold), the erector pilli muscles contract; making the hair follicles to stand erect; The hair follicles trap a layer of hair; between them which reduces heat loss due to poor heat conduction through them; when the temperature is high, the erector pilli muscles relax; thus making the hair to lie flat; thus reducing the air trapped and more heat will be lost to the environment; Skin has sweat glands which secrete sweat; when temperatures are high; water from the sweat evaporates; taking away latent heat of vapourization; when temperature is low, no sweat is produced; When temperature is high, the blood vessels vasadilate; and this encourages loss of heat; as more blood flow close to the skin surface; when temperatures are low, blood vessels vasoconstrict; less blood flows close to skin surface; hence less heat is lost to the environment; Skin has an adipose tissue for insulation against heat loss;
2. Skin has a cornified layer made of dead cells; which protects the entry of bacteria; and inner tissues from mechanical damage; the sebaceous gland, secret sebum; which has antiseptic properties; hence protects the body from bacteria. The skin has melanin pigment; which protect the body from harmful U.V rays;
1. Wind dispersal
  - Some seeds / fruits have parachute (hair like structures extending from the seed coat / fruit wall; which increases the surface area for floating in air; to be blown over a long distance e.g. in sow thistle;
  - Some seeds have papery extensions (winged seed / fruits); to increase the surface for floating in air so that they can easily be carried by wind; e.g. jacaranda; spatholea sp;
  - Some plants have ovaries which are capsule shaped; which on drying up burst open along lines of weakness thus scattering the seed, into the air; This is called censor mechanism e.g. simsim;
  - Some seeds are light in weight; to be easily blown by wind;
2. Animal dispersal
  - Having hooks on the ovary wall or calyx; which stick on the fur / clothes of animals passing by; e.g. black jack fruit; devils horsewhip fruit;
  - Being succulent / fleshy; to attract animals to feed on them as the seeds are dispersed;
  - Seed, having a hard indigestive seed coat; which passes through the animal’s digestive system undigested; e.g. in Guavas;
  - Being brightly coloured when ripe; to attract animals; e.g. oranges, guavas, tomatoes;
  - Being large in size and conspicuous; to be seen by animals easily; e.g. oranges;
3. Water dispersal
  - Having fibrous walls containing many air pockets; for easy floating on water; so that it can
  - be carried by water waves / scattered;
  - Self dispersal mechanism/explosive mechanism
  - Have a line of weakness(suture) that explodes realizing the seeds