KNEC KCSE BIOLOGY TOPICAL QUESTIONS

K.C.S.E Biology Q & A - MODEL 2019PP2QN05

2/7/2020

K.C.S.E Biology Q & A - MODEL 2019PP2QN05

A person accidentally touches a hot pan and responds as illustrated in the diagram below.

(a) Explain how the response illustrated above occurs.
(b) Explain how auxins are utilised as selective weed killers in agriculture.

answers

(a) The stimulus /heat/pain is detected by temperature/pain receptor( Thermo receptors) in the skin/dermis; An impulse is generated; impulse is transmitted along a sensory neurone to the CNS/spinal cord; (chemical) transmission across synapse to relay neurone; Across a synapse to motor neurone; across a synapse to biceps muscles,/effector via motor neurone; muscles/effectors contracts; (hand moves away). This is known as (simple reflex action);
Stimulus/pain/temperature detector
Receptor-impulse-sensory neurone-synapse-relay neurone (CNS)-synapse-motor neurone- synapse-biceps-control.
(b) Selective weed killer contains auxins which are absorbed by the weeds (than desired/ beneficial plants); making the weeds to grow abnormally/accelerated die out; (weed of the beneficial plants);

Comments

K.C.S.E Biology Q & A - MODEL 2019PP1QN10

1/7/2020

Comments

K.C.S.E Biology Q & A - MODEL 2019PP1QN10

In an investigation, students set up the apparatus below in the laboratory and made observations after 72 hours.

(a) Explain how inclusion of the following components would affect the mouse in the experiment:
(i) light
(ii) sodium hydroxide solution
(b) State why the students preferred to use a bell jar and not a tin box in the experiment.

answers

.(a) i) light enables the potted plant to photosynthesize; producing oxygen which is
Inhaled by the mouse, (sustaining it); the illuminated light can further affect /alter some photosynthesized processes in the mouse as a result of constant direct beam of light.
(ii) Absorbs carbon(iv)oxide (mainly exhaled by the mouse); while at the same time deny the plant the needed raw material, carbon (iv) oxide to photosynthesize hence suffocating the mouse/ emitting its survival / no oxygen;
(b) bell jar is transparent, allow penetration of light for the plant to photosynthesize; tin box is opaque hence does not allow photosynthesis/ could easily heat up altering the temperature inside for the mouse/ plant;

Comments

K.C.S.E Biology Q & A - MODEL 2019PP2QN05

K.C.S.E Biology Q & A - MODEL 2019PP2QN05

K.C.S.E Biology Q & A - MODEL 2019PP1QN10

K.C.S.E Biology Q & A - MODEL 2019PP1QN10

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