Plant and Animal Responses OCR A-Level Biology

Cytokinins

Promote cell divison

Delay leaf sensescense

Overcome apical dominance

Promote cell expansion

abscisic acid

inhibits cell growth, helps close stomata

Auxins

Promote cell elongation

Inhibit growth of side shoots

Inhibit leaf fall

Gibberellins

Promote stem and leaf elongation

Ethene

Promotes fruit ripening

How do gibberellins work?

They travel to the aluerone layer in the endosperm of the seed, where they enable the production of amylase that breaks down starch to glucose for use in respiration by the embryo so it can grow

What are the different types of meristem?

Apical: riots and shoots to make them longer

Lateral Bud: gives rise to side shoots

Lateral: form cylinders near the outside of roots and shoots so they can grow wider

Intercalary: between nodes so the shoot can grow longer

How does auxin stimulate cell growth?

Increases extensibility of cell wall

What are the commercial uses of auxin ?

Prevent lead and fruit drop

Promote flowering

Herbicides

Seedless fruit

Cytokinins commercial uses

Mass produce plants

Delay leaf senescence

Prevent yellowing leaves

Commercial uses of gibberellins

Delay senescence of citrus fruit

Improve shape of apples

Elongate grape and sugar stalks

Induce seed formation in young trees

Speed process of producing malt

Commercial uses of ethene

Speed fruit ripening

Promote fruit drop

Promote female sex expression in cucumbers

Promote lateral growth in plants

What is the PNS divided into?

The sensory system and the motor system which is further divided into the:

Somatic Nervous System (SNS)

Autonomic Nervous System (ANS)

What is the CNS composed of?

Brain and spinal cord, both of which have non myelinated neurones, the spinal cord having more myelinated ones for more rapid conduction of action potentials

What is the role of the sensory nervous system

Conducts action potentials from sensory receptors to the CNS

What does the motor nervous system do?

Conducts action potentials from the CNS to effectors

What is the difference between the autonomic and somatic nervous systems?

The somatic system carries action potentials under voluntary control mostly my myelinated neurones (faster) and the autonomic conducts action potentials not under voluntary control and mostly by non myelinated neurones

Which system prepares for activity ?

The sympathetic system

What are the 4 main parts of the brain

Cerebrum

Cerebellum

Hypothalamus and Pituitary Complex

Medulla Oblongata

What does the cerebellum do ?

Involved in balance and coordination, coordinates conscious contraction, can programme coordination of certain activities that are learnt through practise

What is the cerebrum for

Higher thought processes, has different areas responsible for different things

Hypothalamus and Pituitary Complex does what?

Maintains the internal environment using osmoregulation and temperature regulation

What does the medulla oblongata do ?

Controls non-skeletal muscles by sending action potentials through the autonomic nervous system

Contains centred for controlling heart rate, circulation and breathing

What are reflexes?

These are rapid, predictable, and involuntary responses to stimuli

corneal reflex

Eye blinks very rapidly, mediated by a sensory neutrons that enters the pons

Knee jerk reflex

Spinal reflex, only two neurones involved so very quick

How is the fight or flight response coordinated ?

Inputs feed into the cerebrum which passes signals to association centres. If a threat is recognised the cerebrum stimulates the hypothalamus which increases activity in the sympathetic nervous system

How does adrenaline work ?

It binds to an adrenaline receptor on the plasma membrane, which stimulates a G protein to activate adenyl Cyclase. Adenyl cyclase converts ATP to cAMP which is the second messenger and causes enzyme action in the cell

What is the SA node?

The pacemaker of the heart. Initiates the action potential that is conducted through the heart.

How is heart rate reduced/increased

Action potentials sent down accelerator (sympathetic) nerves cause the release of noradrenaline to increase heart rate

Action potentials sent down vagus (parasympathetic) neves cause the release of acetylcholine to reduce heart rate

What do stretch receptors do?

Detect movement of limbs and increase heart rate

What do chemoreceptors do?

Monitor the pH of blood

Describe involuntary (smooth) muscle

Contracts slowly and regularly

Found in walls of tubular structures

Arranged in layers that oppose each other

Individual spindle shaped cells

Describe cardiac muscle

Striated, uninucleated, branching

Cells are joined by intercalated discs that allow diffusion of ions between cells

Contracts and relaxes continually

Does not fatigue easily

Myotonic - initiates it's own contraction

Describe voluntary (skeletal) muscle

Occurs at joints in the skeleton

Arranged in antagonistic pairs

Fibres are multi nucleic and surrounded by the sarcolemma

Muscle cell cytoplasm is sarcoplasm which contains lots of mitochondria and sarcoplasmic reticulum

Contents of fibres are in myofibrils

Describe the action at a neuromuscular junction

Action potentials at the end of an axon open calcium ion channels allowing the ions to flood into the tip. Vesicles of acetylcholine move towards the membrane and fuse before diffusing across the gap and bring to receptors. Sodium channels open and sodium ions enter the muscle fibre causing a wave of depolarisation which passes along the sarcolemma down transverse tubules

What are myofibrils?

bundles of thick and thin filaments

Thick: dark band

Thin: light band

What is a sarcomere?

The distance between two Z lines

Describe the light band

Two chains of actin twisted around tropomyosin with troponin molecules attached to it

Describe thick filaments

They are assembled from bundles of the protein molecule, MYOSIN.

sliding filament theory

theory on the mechanism for muscle contraction, caused by myosin heads attaching to actin and moving

What is the role of ATP is muscle contraction

Supplies energy, myosin head can hydrolyse ATP to ADP and inorganic phosphate releasing energy in a power stroke