6 - RESPONDING TO CHANGES IN THE ENVIRONMENT Flashcards
Generally, how is the heart rate controlled?
- internal stimuli detected by pressure receptors (baroreceptors) in the aorta and carotid arteries
- chemical receptors in the aorta, carotid arteries and medulla monitor O2 level in blood as well as pH and CO2 (these are indicators of O2 levels)
- electrical impulses sent from receptors to medulla along sensory neurones
- medulla processes info and sends impulses to SAV along sympathetic or parasympathetic neurones.
What are taxis and kinesis?
Taxis - an organisms directional movement in response to a stimulus to keep them in a favourable environment
Kinesis - non directional random movement in response to a stimulus
What is phototropism?
The growth of a plant in response to light
- shoots are positively phototropic (grow towards light)
- roots are negatively phototropic (grow away from light)
What is Gravitropism?
The growth of a plant in response to gravity
Shoots are negatively gravitropic (grow upwards)
Roots are positively gravitropic (grow downwards)
What is an auxin?
Any group of hormones that regulate plant growth
Give an example of an auxin
Indoleacetic acid (IAA)
- produced in the tips of the shoots and roots in flowering plants
- It’s moved around the plant to control troop prims and it moves by diffusion and active transport over short distances via the phloem
- This results in different parts of the plant having different concentrations IAA the uneven distribution of IAA means there’s uneven growth of the plant
E.g.
IAA concentration increases on the shaded side of a shoot, cells elongate and the shoot bends towards the light
What is visual acuity?
What type of visual acuity do rods and cones have?
The ability to tell two points apart that are close together
- rods give low visual acuity because many rods join the same bipolar neural so light from two points close together can’t be told apart
- cones have high visual security because each cone joins its own bipolar neuron. when light from two points hits two cones, two action potentials go to the brain so you can distinguish two points close together as two separate points
What is visual acuity?
The ability to tell apart points that are close together
Rods have low visual acuity because many rods join the same bipolar neurone
Cones have high visual acuity because each cone joins its own bipolar neurone
Describe the structure of a pacinian corpuscle and what their function is
- A sensory nerve ending joined to a sensory neurone
- Lamellae surrounding the sensory nerve ending
- Inside of the membrane is negatively charged compared to the outside
- when pacinian corpuscle is stimulated, e.g a tap on the arm, the lamellae are deformed and press on the sensory nerve ending. This causes the sensory neurones cell membrane to stretch, deforming the stretch mediated sodium ion channels. The channels open and sodium ions diffuse into the cell creating a generator potential, if the generator potential reaches the threshold, it triggers an action potential
What is spatial summation?
- when two or more presynaptic neurones release their neurotransmitters at the same time onto the same post synaptic neurones
- The small amount of neurotransmitter released from each of these neurons can be enough to reach the threshold in the post synaptic neurone and trigger an action potential
What is temporal summation?
- when two or more nerve impulses arrive in quick time from the same pre synaptic neurone
- makes the action potential more likely because more neurotransmitter is released into the synaptic cleft
State the main features of skeletal muscle
Muscle tissue
Sarcolemma - cell membrane of muscle cells
Sarcoplasm - cytoplasms of muscle cells
Transverse tubules - help spread electrical impulses throughout the cell
Sarcoplasmic reticulum - stores calcium ions for muscle contraction
Myofibrils - enable the muscle fibres to contract
Sarcomere - many short units that make up myofibrils
Describe the process of muscle contraction
- arrival of action potential at muscle fibre
- wave of depolarisation passes along the sarcolemma and down the T tubules
- this stimulates the sarcoplasmic reticulum to release stored calcium ions into the sarcoplasm
- influx of calcium ions triggers muscle contraction
- calcium ions bind to a protein attached to tropomyosin causing the protein to change shape
- this pulls the attached tropomyosin out of the actin - myosin binding site on the actin filament
- binding site is exposed allowing myosin head to bind (forming a cross bridge)
- calcium ions also activate ATP hydrolase to break down ATP into ADP + Pi
- energy released from ATP causes the myosin head to bend, pulling the acting in a rowing movement
- another ATP provides the energy to break the cross bridge
- myosin returns to start position and then binds to different binding site, process repeats
When the muscle stops contracting, calcium ions leave their binding sites and move back to the sarcoplasmic reticulum by active transport
How is a generator potential reached?
- when a stimulus is detected, the cell membrane is excited and becomes more permeable allowing more ions to move in and out of the cell, this changes the potential difference
- The change in potential difference due to a stimulus is called the generator potential
- Biggest stimulus excites the membrane more causing a bigger movement of ions and a bigger change and potential difference so a bigger generator potential is produced
- If the generator potential is big enough, it will trigger an action potential
- An action potential is only triggered if the generator potential reaches a certain level called the threshold level
What is type of diabetes?
The immune system attacks B cells in the islets of langerhans
B cells can’t produce sufficient insulin
After eating, insulin levels rise and stay high
-> need regular insulin injections
