Abiotic components definition:
Components of an ecosystem that are non-living
Alkaloids definition:
Organic, nitrogen-containing bases that have important physiological effects on animals.
Examples of alkaloids:
- Nicotine
- Quinine
- Strychnine
- Morphine
Biotic components definition:
Components of an ecosystem that are living
Pheremone definition:
Any chemical substance released by one living thing, which influences the behaviour or physiology of another living thing.
Tannins definition:
Phenolic compounds, located in a cell vacuole or in surface wax on plants
Tropism definition:
A directional growth response in which the direction of the response is determined by the direction of the external stimulus.
Nastic response definition:
Non-directional and quick response to external stimulus.
What chemicals are used by plants to protect themselves from herbivores?
- Tannins
- Alkaloids
- Pheremones
How do tannins protect plants from herbivores?
- Toxic to microorganisms and larger herbivores
- In leaves they are found in the upper epidermis and make the leaf taste bad
- In roots, they prevent infiltration by pathogenic microorganisms
How do alkaloids protect plants from herbivores?
- Derived from amino acids
- Taste bitter
- Located in growing tops and flowers and peripheral cell layers of stems and roots.
How do pheremones protect plants from herbivores?
Chemical released by plants that can affect the behaviour of physiology of herbivores.
What are examples of types of tropism?
- Phototropism
- Geotropism
- Chemotropism
- Thigmotropism
What is phototropism:
Shoots grow towards the light. This enables them to photosynthesise
What is geotropism?
Roots grow upwards towards the pull of gravity. This anchors them in the soil and helps them to take up water.
What is chemotropism?
On a flower, pollen tubes grow down the style, attracted by chemicals, towards the ovary where fertilisation can take place.
What is thigmotropism?
Shoots of climbing plants, such as ivy, wind around other plants or solid structures to gain support.
Positive tropic response definition:
When a plant responds towards a stimulus
Negative tropic response definition:
When a plant responds away from a stimulus
Example of thigmonastic response:
Venus fly trap closing leaves.
Where are plant hormones produced?
By cells in a variety of tissues in the plant
Examples of plant hormones:
- Cytokinins
- Abscisic acid
- Auxins
- Gibberellins
- Ethene
What do cytokinins do?
- Promote cell division
- Delay leaf senescence
- Overcome apical dominance
- Promote cell expansion
What does abscisic acid do?
- Inhibits seed germination and growth
- Causes stomatal closure when the plant is stressed by low water availability
What do auxins do?
- Promote cell elongation
- Inhibit growth of side-shoots
- Inhibit leaf abscission (leaf fall)
What do gibberellins do?
-Promote seed germination and growth of stems
What does ethene do?
Promote fruit ripening
How do hormones travel around the plant?
- Active transport
- Diffusion
- Mass flow in the phloem sap or xylem vessels
Apical dominance definition:
Inhibition of lateral buds further down the shoot by chemicals produced in the apical bud at the top of the plant shoot
Auxins definition:
Plant hormones which are responsible for regulating plant growth
Gibberellins definition:
Plant hormones which are responsible for stem elongation and seed germination
What happens when you break she shoot tip (apex) off the plant?
The plant starts to grow side branches from lateral buds that were previously dormant
What did researchers do the show that auxins in the apical bud prevent lateral buds from growing?
Applies a paste containing auxins to the cut end of a shoot and the lateral buds did not grow
How did scientists prove that it was auxin causing lateral buds not to grow, and not a hormone being produced when the tip was exposed to oxygen?
Applied a ring of auxin transport inhibitor below the apex of the shoot and the lateral buds grew.
What hormones other than auxin are involved in plant growth?
- Abscisic acid
- Gibberellins
What does abscisic acid do?
- Inhibits bud growth
- High auxin in the shoot may keep abscisic acid levels high in the bud
- When the tip is cut (source of auxin), abscisic acid levels will drop so the bud will start to grow.
What do cytokinins do?
-Promote bud growth
-Directly applying cytokinin to buds can overide apical dominance
-High levels of auxin in the shoot apex make most of the cytokinin go there
When the apex is removed, the cytokinin travels evenly around the plant, causing lateral growth.
What happens when gibberellic acid is applied to dwarf varieties of plants?
They grow taller
How was the function of gibberellin proved?
By comparing the concentrations of GA1 (gibberellin) in tall and short pea plants. Tall pea plants had a higher concentration
What converts GA20 to GA1?
An enzyme produced by the Le gene
How was it proven that GA20 can be converted into GA1?
- Researchers chose a pea plant that blocks part of gibberellin production so GA20 can not be made
- The researchers grafted a shoot onto a homozygous lele plant (which cannot convert GA20 into GA1) and it grew tall
- This is because although the shoot had no GA20, it still had the enzyme to convert GA20 into GA1
- Because this shoot grew tall, it confirms GA1 causes cell elongation
How does gibberelllin work?
- GA1 moves through plasma membrane
- Binds to receptor proteins as part of a chain reaction
- DELLA protein normally binds to transcription factors, rendering them useless, but the GA1 breaks down the DELLA
- Once the DELLA is gone, the transcription of a growth gene can occur
How does gibberellin promote seed germination?
- Gibberellin is released when the seed absorbs water
- The gibberellin travels to the aleurone layer on the endosperm region of the seed
- The gibberellin enables the production of amalayse, which breaks down starch into glucose
- This then enables the embryo to respire and grow
- The glucose is also used for protein synthesis
What are apical meristems?
Meristems at the tips or apices of roots and shoots. Responsible for roots and shoots getting longer
What are lateral bud meristems?
Meristems found in the buds. These can cause side shoots to grow
What are lateral meristems?
Form a cylinder near the outside of roots and shoots. Cause them to get wider
What are inrercalary meristems?
Found in some plants between the nodes where the leaves and buds branch off the stem. Growth between the nodes is responsible for the shoots getting longer
How did Darwin’s experiment to shoe that the growth stimulus is produced at the tip work?
- Control showing tip growing towards light
- Shoot with tip cut off doesn’t grow towards light
- Shoot with tip covered doesn’t grow towards light
What were the conclusions made from Darwin’s experiment to show the growth stimulus is produced at the tip?
- Light dependant stimulus in the tip
- Growth stimulus travels to zone of elongation
- The cells on the shaded side grow more than those on the sunny side
How did Boysen-Jensen prove that the thing causing shoots to bend (auxin) is soluble in water?
- Sheet of mica through shady half causes it to stop bending, but when in sunny half it still bends
- When tip is cut off and placed back on top of gelatin it still bends
What are the conclusions about Boysen-Jensen’s experiment about the thing causing plant shoots to bend (auxin) being soluble?
- Something has to travel to the shady side for the shoot to bend
- It’s soluble
How did Went prove that it was auxin causing shoots to bend and that the more auxin there was, the more the shoots would bend?
- Tips placed on agar so auxin diffuses into agar
- Agar blocks put on shoots with removed tips, in the dark
- The shoots bend
What are the conclusions made from Went’s experiment about auxin causing plant shoots to curve?
- Something in the tip which causes it to bend
- Concentration dependant as more blocks cause it to bend more
What can artificial auxins be used for?
- Prevent leaf and fruit drop
- Rooting powder
- Creating seedless fruit
- Herbicides
How can auxins be used to create seedless fruit?
Applying auxins promotes ovule growth which triggers the automatic production of auxin by tissues in the developing fruit, helping the complete the developmental process
How can auxins be used to create herbicides?
Because they are man made auxins, plants find them difficult to break down and they can act within the plant for longer. They promote shoot growth so much that the stem cannot support itself so it buckles and dies.
What are the commercial uses for cytokinins?
- Prevent yellow of lettuce leaves as they delay leaf senescence
- Used in tissue culture as they promote bud growth and shoot growth from small pieces of tissue taken from a parent plant
How can gibberellins be used commercially for fruit production?
- Delay senescence in citrus fruits, extending their shelf life
- When acting with cytokinins can elongate apples, improving their shape
- Cause grape stalks to elongate, making the grapes less compact so they grow bigger
How can gibberellins be used commercially to improve brewing?
Speeds up this process:
When barley seeds germinate, the aleurone layer of teh seed produces amylase which brakes down starch into maltose.
After this has been sped up, malt is produced by drying and grinding the seeds.
How can giberellins be used to help sugar production?
Spraying sugar cane with gibberellins stimulates growth between the nodes, making the stems elongate.Sugar is stored in the cells of the internodes so this makes more sugar available from each plant
How are gibberellins useful for plant breeding?
- Speed up reproduction levels by inducing seed formation in young trees
- Spraying plants with gibberellin synthesis inhibitors keeps plants short and stocky.
How is spraying ethene used commercially?
it’s a gas so converted to 2-chloreothylposphonic acid which can be sprayed in solution and is easily absorbed
- Speeds up fruit ripening in apples, tomatoes and citrus fruits
- Promotes fruit drop in cotton, cherry and walnut
- Promotes female sex expression in cucumbers, reducing the chance of self polination (makes cucumbers taste bitter) and increases yield
- Promotes lateral growth in some plants, yielding compact flowering stems
How is reducing ethene’s effects useful commercially?
Storing fruit at a low temperature with little oxygen and lots of carbon dioxide prevents ethene synthesis and thus prevents fruit ripening, so fruit can be stored for longer
Autonomic nervous system definition:
Part of the nervous system responsible for controlling the involuntary motor activities of the body
Central nervous system definition:
The central part of the nervous system, composed of the brain and spinal chord
Peripheral nervous system definition:
The sensory and motor nerves connecting the sensory receptors and effectors to the CNS
Somatic nervous system definition:
The motor neurons under conscious control
What is the autonomic nervous system divided into?
Sympathetic and parasympathetic systems
What are the features of the sympathetic system?
- Many nerves leading out of CNS
- Ganglia just out of CNS
- Short pre-ganglionic nerves
- Long post-ganglionic nerves
- Uses noradrenaline as the neurotransmitter
- Increases activity- prepares body for activity
- Most active at times of stress
What are the features of the parasympathetic system?
- Few nerves leading out of CNS
- Ganglia in effector tissue
- Long pre-ganglionic neurones
- Short post ganglionic neurones
- Uses acetylcholine as the neurotransmitter
- Decreases activity- conserves energy
- Most active during sleep or relaxation
What are examples of effects of the sympathetic system?
- Increased heart rate
- Dilated pupils
- Increased ventilation rate
- Reduces digestive activity
- Orgasm
What are examples of effects of the parasymathetic system?
- Decreased heart rate
- Constricted pupils
- Reduced ventilation rate
- Increased digestive activity
- Sexual arousal
Cerebellum definition:
Region of the brain coordinating balance and fine control of movement
Cerebrum definition:
Region of the brain dealing with higher functions such as conscious thought; it is divided into two hemispheres
Hypothalamus definition:
The part of the brain that coordinates homeostatic response
Medulla oblongata definition:
Region of the brain that controls physiological processes
Pituitary gland definition:
Endocrine gland at the base of the brain, blow but attached to the hypothalamus. The anterior lobe secretes many hormones. The posterior lobe stores and released hormones bade in the hypothalamus
Corpus callosum definition:
Connects the two hemispheres of the cerebrum
Cerebral cortex defintion:
Outermost layer of the cerebrum consisting of a thin layer of nerve cell bodies.
Reflex action definition:
A response that does not involve any processing by the brain
What is the order of neurones?
- Sensory neurone
- Relay neurone
- Motor neurone
What are the two types of blinking reflex?
- Corneal reflex
- optical reflex
How does the corneal reflex work?
- Sensory neurone from the cornea which enters the pons
- Sensory - relay - motor
- Motor neurone passes back out of the brain to the facial muscles, causing the eyelid to blink
- Short and direct pathway so very rapid (0.1 seconds)
- Cranial reflex
How can the corneal reflex be overridden?
- There is an inhibitory neurone that goes to the higher parts of the brain
- This neurone is myelinated and the relay neurone is not, so the inhibitory action potentials can prevent the formation of action potentials in the motor neurone, as the inhibitory neurone is faster than the relay neurone
How does the optical reflex work?
- Protects light sensitive cells of the retina from damage
- Mediated by the optical centre in the cerebral cortex
- Slower than the corneal reflex
How does the knee jerk reflex work?
- Spinal reflex
- Involved in coordinating movement and balance
- When the muscles at the front of the thigh are stretched, specialised stretch receptors (muscle spindles) detect the increase in length of the muscle
- If this stretching is unexpected, it causes contraction of the same muscle
Why can’t the knee jerk reflex be overridden?
There is no relay neurone
Adenyl cyclase definition:
An intracellular enzyme, which is activated by certain hormones
Cyclic AMP (cAMP) definition:
A secondary messenger released inside cells to activate a response
What physiological changes can occur in the fight or flight response?
- Pupils dilate
- Heart rate and blood pressure increases
- Arterioles to the digestive system and skin are constricted, whilst those to the muscle and liver are dilated
- Blood glucose levels increase
- Metabolic rate increases
- Erector pili muscles in the skin contract
- Ventilation rate and depth increase
- Endorphins (natural pain killers) are released from the brain
Why does metabolic rate increase in the fight or flight response?
Converts glucose to usable forms of energy such as ATP faster
Why do erector pili muscles in the skin contract in the fight or flight response?
Makes hairs stand up which is a sign of aggression
Why are endorphins (natural pain killers) released during the fight or flight response?
Wounds inflicted on the mammal do not prevent activity
How are threats detected?
- Inputs fed into the sensory centres in the cerebrum
- The cerebrum passes signals to association centres
- If a threat is recognised, the cerebrum stimulates the hypothalamus
- The hypothalamus increases activity in the sympathetic nervous system and stimulates the release of hormones from the anterior pituitary gland
What part of the nervous system can achieve long responses?
The endocrine system
What is the first messenger in the mechanism of adrenaline action?
Adrenaline
Why can’t adrenaline enter the target cell?
It is an amino acid derivative
What happens in the mechanism of adrenaline action?
- Adrenaline binds to the adrenaline receptor on the plasma membrane
- This receptor is stimulated with a G protein on the inner surface of the plasma membrane which is stimulated to activate adenyl cyclase
- Adenyl cyclase converts ATP to cAMP which is the second messenger inside the cell
- cAMP causes an effect inside the cell by activating enzyme action. The precise effect depends on which cell the adrenaline has bound to.
What is the second messenger in the mechanism of adrenaline action?
Cyclic AMP (cAMP)
How are releasing factors secreted from the hypothalamus?
- They are released into the blood
- They pass down a portal vessel to the pituitary gland and stimulate the release of topic hormones from the anterior of the pituitary gland
- These stimulate activity in a variety of endocrine glands
What does Corticotropin-releasing hormone (CRH) do?
- From the hypothalamus
- Causes the release of adrenocorticotropic hormone (ACTH)
What does adrenocorticotropic hormone (ACTH) do?
- Passes around in the blood system
- Stimulates the adrenal cortex to release a number of different corticosteroid hormones
- As a result, more glucose is released from glycogen stores.
- New glucose may also be produced from fat and protein stores
What does Thyrotropin-releasing hormone (TRH) do?
Causes the release of thyroid-stimulating hormone (TSH)
What does thyroid-stimulating hormone (TSH) do?
-Stimulates the thyroid gland to release more thyroid hormone (thyroxine) which acts on nearly every cell of the body, increasing the metabolic rate and making the cells more sensitive to adrenaline
Examples of hormones released from the anterior pituitary gland?
- Corticotropin-releasing hormone (CRH)
- Thyrotropin-releasing hormone (TRH)
What are the functions of the circulatory system?
- Transport of oxygen and nutrients
- Removal of waste products
- Transport of urea from liver to kidneys
- Distribute heat around body or deliver it to the skin to be radiated away
What are the different ways heart action can be modified?
- Altering the heart rate (bpm)
- Altering the force of contractions of the ventricular walls
- Altering the stroke volume (volume of blood pumped per beat)
What is the frequency of the excitation waves controlling heart rate controlled by?
The cardiovascular centre in the medulla oblongata
How does the cardiovascular centre in the medulla oblongata alter the frequency of excitation waves over the ventricle walls?
- Action potentials sent down the accerans nerve (sympathetic system), causing the release of the neurotransmitter noradrenaline at the SAN, increasing heart rate
- Action potentials sent down vagus nerve (parasympathetic system), causing the release of the neurotransmitter acetylcholine at the SAN, reducing heart rate
Where do signals about the environmental factors affecting heart rate get sent to?
The cardiovascular centre in the medulla oblongata
Examples of sensory input to the cardiovascular centre:
- Stretch receptors in the muscles
- Chemoreceptors in the cartoid arteries, aorta and brin monitor the PH of the blood
- Concentration of carbon dioxide in the blood
- Stretch receptors in the carotid sinus monitor blood pressure
Cardiac muscle definition:
Muscle found in the heart walls
Involuntary muscle definition:
Smooth muscle that contracts without conscious control
Neuromuscular junction definition:
The structure at which a nerve meets the muscle, it is similar in action to a synapse
Skeletal (striated) muscle definition:
Muscle under voluntary control
Structure of involuntary (smooth) muscle:
- Individual cells tapered at both ends (spindle shaped)
- At rest, 500um long and 5um wide
- Each cell contains a nucleus and bundle of actin and myosin
- Arranged in longitudinal and circular layers that oppose each other
Where is involuntary muscle found?
Walls of tubular structures e.g. digestive system and blood vessels
What part of the nervous system controls smooth muscle?
Autonomic
Structure of cardiac muscle:
- Individual cells form long fibres which branch to form cross bridges between fibres
- The cross bridge helps to ensure the electrical stimulation spreads evenly over the walls of the chambers
- When the muscle contracts, this arrangement also ensures that the contraction is a squeezing action
- The cells are joined by intercalated discs which are specialised cell surface membranes fused to produce gap junctions that allow free diffusion of ions between cells
How does cardiac muscle appear when viewed under a microscope?
Striped
Sarcolemma definition:
The membrane surrounding voluntary muscle fibre
How long is each voluntary muscle fibre?
100um in diameter
Sarcoplasm definition:
Muscle cell cytoplasm
How is sarcoplam specialised?
- Multinucleic (voluntary muscle)
- Many mitochondria
- Many ribosomes
What is the contents of fibres in voluntary muscle arranged into?
Myofibrils
What are myofibrils divided into?
Sarcomeres
In sarcomeres, what are the dark bands?
A bands
In sarcomeres, what are the light bands?
I bands
How does the neuromuscular junction work?
- Action potentials arrive at end of axon of motor neurone and open calcium ions channel in the membrane, causing calcium ions to flood to the end of the axon
- Vesicles of acetylcholine move towards and fuse with end of membrane
- Acetylcholine molecules diffuse across gap and fuse with receptors in the sarcolemma
- This open sodium ion channels, so sodium enters the muscle fibre, causing depolarisation of the sarcolemma
- Wave of depolarisation travels along sarcolemma and down transverse tubules into muscle fibre
- Calcium ions flood muscle fibres
- Troponin altered and tropomysin shifts
- Myosin-actin binding site opens
- Contraction begins
Motor unit definition:
Many motor neurones divide and connect to several muscle fibres. All muscle fibres contracting again causes a stronger force
Creatine phosphate definition:
A compound in muscle that acts as a store of phosphates and can supply phosphates to make ATP rapidly
What is the end line of a sarcomere#?
Z line
What is the part of the sarcomere in the middle of the dark band where there is no overlap?
H zone
How long is a sarcomere at rest?
2.5um
Structure of thin filaments:
- Made of two actin subunits twisted around each other
- Wound around the actin is a molecule of tropomyosin
- Globular molecules of troponin are attached to the tropomyosin
Structure of troponin:
- Each troponin complex consists of three polypeptide chains
- One binds to actin
- One binds to tropomyosin
- One binds to calcium when it is available
What does tropomyosin do at rest?
Cover the binding sites for thick filaments
Structure of thick filaments:
- Bundle of myosin molecules
- Each myosin molecule has two protruding heads which stick out at the end of each molecule
- These heads are mobile and can bind to the actin when the binding sites are exposed
Control of contraction:
- When the muscle is stimulated, the AP passes along the sarcolemma and down the t-tubules into the muscle fibre
- AP carried to the sarcoplasmic reticulum which stores calcium ions and causes the release of calcium ions into the sarcoplasm
- Calcium ions bind to troponin, which alters the shape, pulling tropomyosin aside, exposing the binding sites on the actin
- Myosin heads bind to the actin, forming cross bridges between the filaments
- The myosin heads move, pulling the actin filament past the myosin fillament
- The myosin heads detach from the actin and can bind again further up the actin filament
How is ATP for contraction produced?
- The myosin head attaches to the actin filament, forming a cross bridge
- The myosin head tilts backwards, causing the thin filament the slide past the myosin filament. This is the power stroke
- During the power stroke, ADP and Pi are released from the myosin head
- After the power stroke, a new ATP molecule attaches to the myosin head, breaking the cross bridge
- The myosin head then returns to its original position (swings forward), as the ATP is hydrolysed, releasing the energy to make this movement occur
- The myosin head can now make a new cross bridge further along the actin filament
What does the part of the myosin head acting as ATPase do?
Hydrolyses ATP to ADP and Pi (inorganic phosphate), releasing energy
What are the three mechanisms involved in maintaining the supply of ATP?
- Aerobic respiration in mitochondria
- Anaerobic respiration in the sarcoplasm of the muscle tissue
- Creatine phosphate in the sarcoplasm
