2) Structure and functions in living organisms - coordination & response Flashcards
Organs of excretion
-kidney - excretion of urea, water, mineral ions
-lungs - excretion of carbon dioxide, water
-skin - excretion of excess mineral ions
-liver - breakdown of proteins (amino acids) into urea
Homeostasis
Control or regulation of the internal conditions of a cell or organism
-water content, temperature, pH, blood pressure, blood glucose concentration
Tropisms
The directional growth responses made by plants in response to light and gravity
Phototropism - response to light
Geotropism - response to gravity
Auxins
Plant growth regulators that plants produce to coordinate and control directional growth responses
-produced in the tips of the shoots and the roots and diffuse to the cells below the tips
Positive/ negative tropism
-positive tropism - growth towards the stimulus
-negative tropism - growth away from stimulus
Geotropism
Growth towards or away from gravitational pull
-positive: growth towards gravity (roots)
-negative: growth away from gravity (shoots)
Phototropism
Growth towards or away from source of light
-positive: growth towards from light (shoots)
-negative: growth away from light (roots)
Auxins in shoots
Promote cell elongation
-affected by light and gravity
Auxins in roots
Inhibit cell elongation
-only affected by gravity
Auxin - geotropism in shoots
- Auxin accumulates along lower side due to gravity
- Lower side grows faster than upper side as there are more auxin
- Shoots grow up
Auxin - phototropism in shoots
-if light is evenly spread, auxin spreads evenly, grows upward
1. If light is on one side,, auxin diffuses away from the light to the shady side
2. Sunlight breaks down auxins, so exposed sides will have less auxins
3. Side with auxins grow faster
4. Shoot grows towards light
Auxin - geotropism in roots
- Auxin diffuses to the lower side of the route in response to gravity
- Auxins in roots inhibit growth, so lower side grows slower
- Creates downward bend
-roots need to grow down so the plant can absorb water and mineral ions from the soil, and also is anchored to the ground and made stable
Two control systems in humans
-nervous system
-hormonal system/ endocrine system
The nervous system vs endocrine system
Nervous system: use nerve impulses to react quickly to a stimulus
-effectors: muscles/ glands
-very fast
-consists of brain, spinal cord (Central Nervous System) and all the nerves in the body (Peripheral Nervous System)
Hormonal system: use hormones to react slowly to a stimulus
-effectors: target cells in specific tissues
-slower
The Central Nervous System
-nerves spread out from the CNS to all other regions of the body
-CNS acts as a central coordinating centre for the impulses that come in from or are sent out to any part of the body
Neurone structure
-have a cell body - nucleus and main organelles
-axons/ dendrites - cytoplasmic extensions from this body
-axon - main long fibre of the neurone
-insulated by a fatty myelin sheath with small uninsulated sections along its length (nodes)
–electrical impulse does not travel down the whole axon, jumps from one node to the next
-dendrites - extend out from the cell body of the neurone and at the far end of the axon
–neurones can connect to many other neurones and receive impulses from them, forming a network for easy communication
Types of neurones
-sensory neurones
-relay neurones
-motor neurones
Sensory neurones
-carry impulses from sense organs to the CNS
-long
-have a cell body branching off the middle of the axon
Relay neurones
-found inside the CNS and to connect sensory and motor neurones
-short
-have a small cell body at one end with many dendrites branching off it
Motor neurones
-carry impulses from the CNS to effectors
-long
-have a large cell body at one end with long dendrites branching off it
Nervous system pathway
Stimulus –> receptor –> coordination –> effector –> response
Receptors
-detect change in environment
-change energy of the stimulus into electrical energy - transduction
-all receptors are transducers of energy
Effectors
Organs which brings about a response
Role of neurotransmitters
-neurones do not come into direct contact with each other
-dendrites of two neurones meet to make a connection - synapse formed
-synapse - small gap
-electrical signal is briefly converted to a chemical signal that can cross the gap
-chemical signaling molecules used to transfer signal between neurones at a synapse - neurotransmitters
How an impulse passes across a synapse
- An electrical nerve impulse travels along the first axon
- When nerve impulses reach the dendrites, neurotransmitters are released
- Chemicals diffuse across the synapse
- Chemicals bind with receptor molecules on the second neuron
- Binding stimulates the second neuron to transmit an electrical impulse along a neuron
Reflex arc
-a change which happens very quickly, and without conscious thought
Stimulus –> receptors –> sensory neuron –> relay neuron –> motor neuron –> effector –> response
Reflex arc description
- Receptor in the skin detects a stimulus
- Sensory neurons sends electrical impulses to a relay neuron
- Relay neuron connect sensory neurones to motor neurones
- Motor neurons send electrical impulses to an effector
- Effector produces a response (muscles contracts to move hand away)
Receptor cells in the eye
Two types:
-rods - sensitive to light
-cones - detect colour
Structure of a human eye
-cornea
-iris
-lens
-optic nerve
-retina
-aqueous humour
-vitreous humour
-ciliary muscles
-sclera
-pupil
-suspensory ligaments
Cornea
Transparent lens that refracts light as it enters the eye
Iris
Controls how much light enters the pupil
Lens
Transparent disc that can change shape to focus light onto the retina
Retina
Contains light receptor cells - rods and cones
Aqueous humour
Maintains pressure in the eye and nourishes the cornea
Vitreous humour
Maintains the shape of the eye and attaches to the retina
Ciliary muscles
A ring of muscle that contracts and relaxes to change the shape of the lens in accomodation
Sclera
Tough outer layer of the eye. It helps protect the eye from injury
Pupil
Hole in the center of the eye that lets light in
Optic nerve
Bundle of sensory neurones that carry the impulse to the brain
Suspensory ligaments
Ligaments that connect the ciliary muscle to the lens
Accomodation
The way the lens focuses on objects
Accommodation - near objects
- The ciliary muscles contract
- the suspensory ligaments loosen
- stops the suspensory ligaments from pulling on the lens, which allows the lens to become fatter
- Light is refracted more
Accommodation - far objects
- The ciliary muscles relax
- the suspensory ligaments tighten
- The suspensory ligaments pull on the lens, causing it to become thinner
- Light is refracted less
Iris reflex - bright light
-pupil constricts (narrows) to prevent too much light from entering the eye and damaging the retina
1. photoreceptors detect change in environment (light)
2. Radial muscles relax
3. Circular muscles contract
4. Pupil constricts (diameter of pupil narrows)
5. Less light enters the eye
Iris reflex - dim light
-pupil dilates (widens) to allow as much light into the eye as possible to improve vision
1. photoreceptors detect change in environment (dark)
2. Radial muscles contract
3. Circular muscles relax
4. Pupil dilates (diameter of pupil widens)
5. More light enters the eye
Skin - temperature regulation
-largest sense organ
-vasodilation/ constriction of skin capillaries
-shivering
-sweating
-erecting/ flattening of hairs
Mechanism of vasodilation/ constriction
-heat exchange occurs at the body’s surface as this is where the blood comes into closest proximity to the environment
-increase heat loss: supply the capillaries in the skin with a greater volume of blood, loses heat to the environment via radiation
-arterioles have muscles in their walls can relax/ contract to allow more or less blood to flow through them
Vasodilation of skin capillaries
-arteriole muscles relax
-cause the arterioles near the skin to dilate
-allow more blood to flow through capillaries
Vasoconstriction of skin capillaries
-muscles in arteriole walls contract
-causes arterioles near the skin to constrict
-allow less blood to flow through capillaries
-reduces heat loss from the blood as it flows through the skin
Sweating
-secreted by sweat glands
-cools the skin by evaporation which uses heat energy from the body to convert liquid water into water vapour
Shivering
-a reflex action in response to a decrease in core body temperature
-muscles contract in a rapid/ regular manner
-metabolic reactions required to power this shivering generate sufficient heat to warm the blood, raise core body temperature
Hairs - cooling mechanism
- The hair erector muscles in the skin relax, causing hairs to lie flat
- This stops them from forming an insulating layer by trapping air and allows air to circulate over skin and heat to leave by radiation
Hairs - warming mechanism
- The hair erector muscles in the skin contract, causing hairs to stand on end
- This forms an insulating layer over the skin’s surface by trapping air between the hairs and stops heat from being lost by radiation
Adrenaline
-‘fight or flight’ hormone
-from adrenal gland
-designed to prepare it for movement
-increase in heart rate and breathing rate - oxygen can deliver to muscle cells
-divert blood flow towards muscles
-dilation of blood vessels inside muscles - more blood can circulate through them
-break down stored glycogen to glucose - ensures a higher blood glucose concentration for increased respiration - provide greater energy for movement
Insulin
-from pancreas
-lowers blood glucose levels
-causes excess glucose in the blood to be taken up by the muscles and liver and converted into glycogen for storage
Testosterone
-from testes
-main sex hormone in males
-development of secondary sexual characteristics in males
Progesterone
-from ovaries
-maintains pregnancy
-maintains the uterus lining to cushion fertilised egg and allow it to develop
Oestrogen
-from ovaries
-main sex hormone in females
-development of secondary sexual characteristics in females
-controls menstrual cycle
ADH source, role, effect
-pituitary gland
-control the water content of the blood
-increases reabsorption of water from urine in the collecting ducts of the kidney
FSH source, role, effect
-pituitary gland
-causes ovary to develop a mature egg cell
-stimulates the development of egg cells in the ovary and the release of oestrogen
