8.2 Reception Of Stimuli

Question 1

Receptor, Receptor cells

Answer 1

Receptor cells that detect stimuli and send impulses to the central nervous system. Many receptors are spread throughout the body, but some types of receptor cells are grouped together into sense organs. Rods and cones are the receptor cells in the eye that detect light.

Question 2

Sense organs

Answer 2

The eye, ear and skin are examples of sense organs. Each contains receptor cells that detect stimuli and send electrical impulses to the central nervous system. Receptor cells in the eye detect light, those in the ear detect sound, and several different types in the skin can detect touch, pressure, pain and changes in temperature.

Question 3

Conjunctiva

Answer 3

Protects cornea

Question 4

Cornea

Answer 4

Bends light

Question 5

Lens

Answer 5

Focuses light on retina

Question 6

Iris

Answer 6

Controls annoy the of light entering the eye

Question 7

Sclera

Answer 7

Protective layer

Question 8

Blind spot

Answer 8

No light sensitive cells where optic nerve leaves the eye

Question 9

Yellow spot (fovea)

Answer 9

Most sensitive part of the retina located within the macula, the central area of the retina

Question 10

Retina

Answer 10

Contains light sensitive cells

Question 11

Vitreous humour

Answer 11

Transparent jelly

Question 12

Choroid

Answer 12

Black layer prevents internal reflection of light

Question 13

Ciliary muscle

Answer 13

Alters thickness of lens for focusing

Question 14

Photoreceptor

Answer 14

A receptor cell that is stimulated by light and enables us to detects changes in our environment. In the human eye photoreceptors are contained in the retina. There are two distinct types, rods and cones.

Question 15

Rod, Rods, Rod cell

Answer 15

A receptor cell, found in the retina of the eye, which is sensitive to light. Rod cells contain a light-sensitive pigment called rhodopsin. When light falls on rhodopsin, it breaks down into retinal and opsin. This reaction leads to the generation of an action potential in a neurone in the optic nerve. Rod cells only give black and white vision but are able to work in dim light conditions.

Question 16

Cone

Answer 16

A receptor cell, found in the retina of the eye, which is sensitive to light. Cone cells contain pigments which are sensitive to light of different wavelengths. Because of this, cones allow colour vision.

Question 17

Bipolar neurone

Answer 17

A type of nerve cell which has a cell body with two long, thin branches. One of these is a dendron which brings impulses to the cell body. The other is an axon which transmits impulses away from the cell body to other neurones. Bipolar cells in the retina of the eye are important in vision

Question 18

Ganglion neurone

Answer 18

A particular type of neurone found in the eye. The rods and cones are located in the retina and they are the photoreceptors. They form synapses with bipolar cells which, in turn, synapse with ganglion neurones. The axons of these ganglion neurones make up the optic nerve, which leads to the brain

Question 19

Rhodopsin

Answer 19

A light-sensitive pigment found in rod cells in the retina of the eye. When light falls on rhodopsin, it breaks down into retinal and opsin. This reaction leads to the generation of an action potential in a neurone in the optic nerve

Question 20

Non-specific cation channel

Answer 20

A channel in the cell surface membrane that allows any positive ions through, such as Na+ and Ca2

Question 21

Glutamate

Answer 21

A neurotransmitter thought to be released by rod cells at their synapses with bipolar neurones in the retina of the eye

Question 22

Dark adaptation

Answer 22

Rhodopsin, the photochemical pigment in the rod cells of the retina, breaks down when it absorbs light. This causes chemical changes within the cell that result in an action potential being generated in the optic nerve. On entering a darkened room, only black is seen because the rhodopsin must be reformed so it can once again be broken down. The reforming of rhodopsin is known as dark adaptation.

Question 23

Phytochrome

Answer 23

Red and far-red light photoreceptor pigment in plants, some bacteria and fungi. When a red photon is absorbed there is a conformational change from the Pr form to the Pfr,

Question 24

Photoperiod

Answer 24

The light period during a day. In
temperate regions the amount of daylight varies
throughout the year. In the winter, it is light for a relatively short part of the day. In the summer, it is light for much longer. Photoperiod affects
many living organisms. It controls when birds migrate, when plants flower, and when some marine worms lay their eggs.

Question 25

Long day plants

Answer 25

Flower when uninterrupted darkness is less than 12hrs. They need Pfr to stimulate flowering.

Question 26

Short day plants

Answer 26

Flower when the period of uninterrupted darkness is greater that 12hrs. Pfr inhibits flowering

Question 27

Day neutral plants

Answer 27

Flowering is not affected by day length

Question 28

Chi-squared test

Answer 28

to determine if an observed set of categorical data differs from the expected using a null hypothesis that there is no significant difference.

Question 29

Greening

Answer 29

Informal term for the changes that
occur in a plant shoot in response to sunlight,
including development of chloroplasts,
inhibition of shoot lengthening, and stimulation
of cotyledon and leaf expansion. The process is
controlled by phytochromes.

Question 30

Internode

Answer 30

length of stem between leaves