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OCR A-level Biology > Plant and Animal Responses > Flashcards

Flashcards in Plant and Animal Responses Deck (95)
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Why might plants respond to stimuli?

In order to improve chance of survival which will increase their chance of having offspring


What could a plant do in response to threat from a herbivore?

Employ chemical defences


Give 3 examples of chemical defences

Tannins - deposited in leaves and are toxic to microorganisms and herbivores, make the leaf taste bad

Alkaloids - derived from amino acids, make plants taste bitter

Pheromones - chemicals released by one individual which can affect the behaviour or physiology of another


What are tropisms?

Directional growth responses of plants


Give 4 examples of different tropisms

Phototropism - grows towards the light

Geotropism - grows away from gravity

Chemotropism - can grow towards or away from a chemical

Thigmotropism - shoots of climbing plants wrap around structures to pull the plant up


What is the name given to the process where a plant grows TOWARDS a stimulus?

Positive tropic response


What is the name given to the process where a plant grows AWAY FROM a stimulus?

Negative tropic response


What is the name given to a non-directional response?

Nastic response


What controls plant responses?

Plant hormones


Give 5 examples of plant hormones


Abscisic acid





What do Cytokinins do?

Promote cell division

delay senescence

overcome apical dominance


What does Abscisic acid do?

Inhibits seed germination

Causes stomatal closure


What do Auxins do?

Promote cell elongation

Inhibit growth of side-shoots

Inhibit leaf abscission


What do Gibberellins do?

Promote see germination

Promote growth of stems


What does Ethene do?

Promotes fruit ripening


Where does growth occur in plants?



What are the 3 types of meristem?

Apical meristem - found in the apex of roots and cause them to grow longer

Lateral bud meristem - found in buds, allow side shoots to grow

Lateral meristem - form a cylinder near the outside of shoots and roots and allow them to grow wider


How could you investigate the effect of phototropism?

There is a test plant and a control plant

The control plant is illuminated equally from all sides, whereas the test plant is only illuminated from 1 side

Leave them to grow for a few days

The test plant will grow towards the light whereas the control will grow straight up


How could you investigate the effect of geotropism?

Plants are positioned perpendicular to the ground

A control plant is placed on a klinostat which spends very slowly meaning gravity has the same effect on all sides of the plant

An experimental plant is left to grow in the perpendicular position

The control will grow straight whereas the experimental plant will bend away from the ground


When light is shining on one side of the shoot, where would the auxins move to?

The shaded side


How does auxin cause the stem to bend?

It promotes active transport of H+ from the membrane into the cell wall

This lowers pH to a level which is optimum for certain enzymes which break down bonds in cellulose causing the cell wall to be less rigid


How is auxin involved in geotropic actions of roots?

If a root is lying flat, auxin accumulates on the lower side of the root, inhibiting cell elongation

The top side continues to grow which causes the root to bend


Give some commercial uses for auxins

Rooting powder, for growing plants promotes root growth

Growing seedless fruit - treating unpollinated flowers with auxin can grow seedless fruit

Herbicides - In high concentrations, they promote soot growth so much that the stem cant support itself and dies


Give a commercial use of Cytokinins

Because they delay leaf senescence, used to prevent yellowing of lettuce leaves after they are picked


Give commercial uses of Gibberellins

Fruit production - they can make fruit last longer in shops and allow fruit to grow bigger

Brewing - Increase the rate of production of malt which comes from barley seeds

Sugar production - increases the length of sugar cane which improves yield


Give commercial uses of Ethene

Speeding up fruit ripening

Promoting fruit drop in cotton, cherry and walnut


How and why might one want to restrict ethene's effects in industry?

Ethene could reduce shelf life of bananas when shipping them from the Caribbean

Storing them at low temperatures with little Oxygen and high Carbon dioxide levels prevents ethene synthesis


What is the role of the nervous system?

To coordinate rapid responses to external stimuli


What are the two parts of the nervous system?

Central nervous system

Peripheral Nervous system


What are the two parts of the peripheral nervous system?

Sensory system

Motor system


What are the two parts of the motor nervous system?

Somatic system

Autonomic System


What is the difference in structure of the cells in white and grey matter in nervous tissues?

White matter contains myelinated neurones, whereas grey matter contains non-myelinated neurones


What is the role of sensory neurones?

To deliver action potentials from sensory receptors to the CNS


What is the role of the somatic motor nervous system?

To conduct action potentials from the CNS to the effector muscles under conscious control

E.g any skeletal muscle


What is the role of the autonomic motor nervous system?

To conduct action potentials from CNS to the effectors that are under subconscious control

E.g the heart or many glands


What are the two parts of the autonomic nervous system?

Sympathetic system

Parasympathetic system


What is the role of the sympathetic nervous system?

To prepare the body for action

e.g fight or flight response


What is the role of the parasympathetic nervous system?

To conserve energy and allow normal vital function


What are the 4 main parts of the brain?

The cerebrum

The cerebellum

The hypothalamus and pituitary complex

The medulla oblongata


What is the role of the cerebrum?

Conscious thought

Conscious action



Factual memory


What is the role of the cerebellum?

Coordination and movement e.g

Maintaining body position
Judging position of objects
Skeletal muscle contraction


What is the name of the area which connects the cerebrum and the cerebellum?

The Pons


What is the role of the hypothalamus and pituitary complex?

Control of Homeostatic mechanisms, e.g

ADH release
Hormonal control


What is the role of the medulla oblongata?

Controls non-skeletal muscle, e.g

Cardiac centre
Respiratory centre
Vasomotor centre - regulates circulation and blood pressure


What is a reflex action?

A response to changes in the environment that don't require any brain processing


What is the function of a reflex action?

To help an organism survive

get out of danger
avoid damage
maintain balence


Why is the blinking reflex referred to as a cranial reflex?

Because the neuronal pathway goes through the brain, however no conscious thought is required


What is a reflex arc?

When the effector and receptor for a reflex are in the same place


What is the name of the reflex when a foreign object touches the eye?

Corneal reflex


What is the name given to the reflex caused when there is a sudden change in light?

Optical reflex


How and why can the corneal reflex be overridden?

Because the sensory neurone also passes an action potential to myelinated neurones in the pons

This then sends it to the cerebral cortex where conscious thought occurs

This can then send inhibitory signals to the pons overriding the signal


What is a spinal reflex?

A reflex that passes through the spinal cord instead of the brain

Means the reflex can happen faster as signals don't need to travel all the way to the brain


Give an example of a spinal reflex

Knee jerk reflex


Why does the knee jerk reflex occur?

There are specialised stretch receptors in the patella tendon which detect when the muscles are stretched

They are known as muscle spindles

When this change is unexpected they cause the quadriceps to contract to straighten the leg

Enables us to balance on one leg


How many types of neurones are involved in the knee jerk reflex?

Only 2

Sensory neurone --> Motor neurone


Can you inhibit the knee jerk reflex?

No, it doesn't pass through the brain so it is impossible to inhibit


Give some physiological changes that occur during the fight or flight response

Pupils dilate

Heart rate and Blood pressure increase

Arterioles to digestives system constrict while those to active muscles dilate

Blood glucose levels increase

Metabolic rate increases

Hairs stand up

Ventilation rate increases

Endorphins released by the brain


Which subdivision of the nervous system does the fight or flight response utilise?

The sympathetic nervous system


How does adrenaline act inside the cell seeing that it is unable to enter the cell itself?

Adrenaline (first messenger) binds to a surface protein on the target cell which is associated with a G protein inside the cell

G protein activates adenyl cyclase which converts ATP to cAMP

cAMP is the second messenger and cause an effect inside the cell


Which part of the brain secretes releasing hormones?



Which part of the brain secretes tropic hormones?

Pituitary gland

(anterior pituitary)


How do the hypothalamus and pituitary gland interact to release hormones?

Hypothalamus secretes releasing hormones into the blood

They pass down a portal vessel to the pituitary gland

These trigger the secretion of tropic hormones from the anterior pituitary gland


How does the hypothalamus-pituitary complex stimulate the adrenal cortex? (named chemicals)

Corticotropin-releasing hormone (CRH) is secreted from hypothalamus

this triggers the release of Adrenocorticotropic hormone (ACTH)

ACTH stimulates the adrenal cortex to release glucocorticoids such as cortisol


Give two examples of hormones released by the hypothalamus and their counterpart that is subsequently released from the pituitary gland

Corticotropin releasing hormone (CRH) and Adrenocorticotropic hormone (ACTH)

Thyrotropin-releasing hormone (TRH) and
Thyroid-stimulating hormone (TSH)


How could a damaged pituitary gland impact ones metabolism? possible symptoms?

Damaged pituitary would not secrete the right amount of thyroid stimulating hormone (TSH)

This would mean less thyroxine is secreted by the thyroid gland (underactive thyroid)

This could make you tired, sensitive to cold, or gain weight


Give 3 ways that heart action can be modified by

Increase or decrease in heart rate

Altering force of contractions of the ventricular walls

Altering stroke volume`


What does the term myogenic refer to?

The ability for a muscle to initiate its own contractions at regular intervals


Which part of the brain controls heart rate?

Medulla oblongata


What sub section of the nervous system is heart rate controlled by?

Autonomic nervous system


Which nerve from the medulla will reduce heart rate?

Vagus nerve


Which nerve from the medulla will increase heart rate?

Accelerans nerve


Give examples of different receptors that will affect heart rate via the medulla

Stretch receptors - detect movement in the limbs and increase heart rate

Chemoreceptors - detect when pH in blood decreases (happens when muscles produce CO2) and increase heart rate

Stretch receptors in Carotid Sinus - detect when blood pressure is too high, reduce heart rate


What is the role of an artificial pacemaker?

To provide electrical impulses to the SAN when it can no longer do it itself

Allows the heart to beat regularly and with the correct strength of contraction


What are the 3 types of muscle?

Involuntary (smooth) muscle

Voluntary (skeletal) muscle

Cardiac muscle


Where might smooth muscle be found?

In the walls of tubular structures such as the digestive system and blood vessels


What sub-division of the nervous system is smooth muscle controlled by?



Describe the structure of smooth muscle

Spindle shaped

Each cell contains a nucleus and bundles of actin and myosin


Describe the structure of cardiac muscle

individual cells form long fibres

Fibres form cross-bridges between each other

Cells joined by intercalated discs, which are specialised membranes which allow the free diffusion of ions


What is the name for a cardiac muscle cell?



What is the role of Purkyne fibres?

Carry electrical impulses in the heart

Coordinate contraction to prevent back flow


What is the name for a skeletal muscle cell?



Describe the structure of a sarcomere


Surrounded by sarcolemma

Contains the sarcoplasm which contains lots of mitochondria and sarcoplasmic reticulum

Contains actin and myosin


Which subdivision of the nervous system controls skeletal muscle?

Somatic nervous system


What is the name given to the area where the muscle joins to the nervous system?

Neuromuscular Junction


Describe the process of an action potential causing a contraction at a neuromuscular junction

Action potential causes Ca2+ to flood the axon tip

This causes acetyl choline vesicles to bind with the membrane and release into the gap

Acetyl choline diffuses and binds to receptors on the muscle which open Na+ channels

Na+ moves in and depolarises the muscle causing contraction


What are myofibrils?

The contractile units of skeletal muscle


What are the two types of protien filament in the myofibril?

Thin filament

Thick filament


What makes up the light band (I-band)?

Thin filaments


What is the Z-line?

Where the thin filaments are held together

They show the ends of the sarcomere


What makes up the dark band (A-band)?

Thick filaments


What is the H-zone?

The area in the dark band where there is no overlap of the thin and thick filaments


Which protein makes up the thin filaments?



What is attached to actin the thin filaments?

A molecule of tropomyosin to which is attached globular molecules of troonin


What protein makes up the thick filaments?


Myosin has two heads which are mobile and will bind to actin when the binding sites are available


What is sliding filament theory and how can it be shown experimentally?

States that during contraction the thin and thick filaments slide past one another.

Can be shown as on a micrograph, during contraction, Light band (I-band) and H-zone get shorter. The Z-lines move closer together and thus the sarcomere shortens.

This shows the the light filament is sliding over the thick filament