Bio paper 2 FINAL

How does light stimulate a response in rods

• Normally rod cells aren’t very polarised and sodium ions move in and out

• This means the rod is constantly depolarised releasing glutamate to the bipolar cell

• Rhodopsin being broken down causes the sodium channels to be blocked

• Neurone becomes hyperpolarised sending neurotransmitter and thus action potential to the bipolar cell

Posterior pituatry

• Releases ADH and oxytocin

Definition of independent assortment

Different possible combinations of maternal and paternal chromosomes

Correlation coefficient

• Investigating an association between two measurements

• The correlation coefficient is a number between -1 and 1

• A negative value for r gives a negative correlation

• If r is below the critical value, you can’t reject the null hypothesis

Chi squared test

• Comparing frequencies and working out the difference

• if p > 0.05 you can’t reject the null hypothesis

Paired t test

• Df = n-1

• When two sets of data are from same individual or have similar group sizes

Unpaired t test

• Df = n1 + n2 -2

• If your t value is larger than critical value then you can reject the null hypothesis

Homologous chromatids Vs sister chromatids

• Homologous chromatids are inherited from each parent they have same siz and similar genetic content however have different Genetics and one is from mother and one is from father

• Sister chromatids are copies of each other and genetically identical

When does crossing over first occur

Prophase 1

Degrees of freedom in the chi squared test

• (r-1)(c-1)

• Where r is rows and c is columns

Stablising selection

• Environmental changes are not occuring

• Any extremes of phenotypes are selected against

• Ie baby birth weight

Directional selection

• Environment changes

• Causes one extreme to become advantageous

• Ie beak size in a drought

Diversifying selection

• Both extremes are selected for while intermediates are selected against

• IE rock pocket mice where dark mice and light mice are advantageous

Homeostasis definition

Maintaining an internal equilibrium

Why is it important that water content is maintained

Prevent osmotic lysis

Negative feedback

self regulatory mechanisms return the internal environment to optimum when there is a fluctuation

Positive feedback

A fluctuation triggers changes that result in an even greater change from the normal

Hormone definition

Signalling molecules released into the blood only acting on cells with receptors (target cells)

Endocrine glands

• Glands in the endocrine system that release hormones straight into the blood

Exocrine glands

• glands that secrete digestive enzymes into where they are used

• Do not enter the blood

Steroid hormones

• Bind to receptors in the cytoplasm or nucleus to form an active receptor-hormone complex

• Complex moves into nucleus and binds directly to DNA acting as a transcription factor

• ie oestrogen or testosterone

Peptide hormones

• Bind to recptor proteins on the surface of the cell

• Activate secondary messengers which initiate cell activity

• ie cAMP

• ie glucagon and adrenaline

What do auxins do

• Involved in trophic responses

• Control cell elongation

• Suppress lateral growth to maintain apical dominance

• Promote root growth

How do auxins promote cell elongation

• IAA causes active transport of H+ ions into cell wall

• This causes pH to decrease and become the right pH for enzymes that break hydrogen bonds between cellulose fibrils

• Makes walls more flexible and water moves in via osmosis

• Cells with higher turgor pressure elongate faster

What do giberrelins do

• stimulate germination

• Stimulate elongation at cell internodes

• Fruit growth

• Rapid flowering

How is germination stimulated

• Seeds absorb water activating embryo to secrete gibberellins

• Gibberellins diffuse to aleurone layer

• Amylose diffuses to endosperm layer from aleurone layer to hydrolyse starch

• Hexose sugars act as respiratory substrate to produce ATP as ‘energy currency’

What do cytokinins do

• Stimulate development of lateral buds by promoting cell division

2 ways plant growth hormones interact

• Synergistically to achieve same effect IE auxins and giberrelins

• Antagonistically with inverse effects IE Axuins and cytokinins

What is phytochrome

• Plant photoreceptor with 2 different forms

  1. Biologically inactive Pr absorbs red light

  2. Biologically active Pfr absorbs far-red light

When is each form of phytochrome most abundant

In darkness : Pr abundant

In sunlight : Pfr abundant

Ratio of Pr to Pfr enables plant to detect how long days are

How does phytochrome control flowering

Pr absorbs red light and converts to Pfr which stimulates flowering

What are long and short day plants

• Long day plants: flower when sunlight hours exceed a critical value

• Short day plants: flower when darkness hours exceed a critical value

What is photomorphogenesis

Pattern of plant growth and development determined by light intensity

How does phytochrome control photomorphogenesis

• Transition from Pr to Pfr controls: localisation of proteins within cells, transcription of certain genes, phosphorylation of proteins.

• Therefore affects: germination, circadian rhythm, flowering

Red light Vs far red light

• Red light converts inactive to active

• Far red light converts active to inactive

Describe the structure of the spinal cord

• Cylindrical bundle of nerve fibres runs from brain stem to lower back surrounded by spinal verterbrae

• Consists of nerve tissue (neurons, glia, blood vessels)

• Grey matter: H-shaped region contains neurons

• White matter mylenated axons

Medulla oblongata

Controls breathing and heart rate

Cerebellum

Controls balance and coordination of movement

located at the back of the brain

Cerebrum

Initiates movement

Two hemispheres

Hypothalamus

Temperature regulation and osmoregulation

Sympathetic nervous system

• Fight or flight

• Noradrenaline

• Fast response

Parasympathetic nervous system

• Rest and digest

• Acetylcholine

Stages in generating an action potential

1. Depolarisation

2. Repolarisation

3. Hyperpolarisation

4. Return to resting potential

Describe the additional features of a myelinated motor neuron

• Schwann cells wrap around axon many times

• Myelin sheath; made from myelin-rich membranes of Schwann cells

• Nodes of Ranvier; very short gaps between neighbouring Schwann cells where there is no myelin sheath

Why do myelinated axons conduct impulses faster than unmyelinated axons

saltatory conduction: impulse ‘jumps’ from one node of Ranvier to another

in an unmyelinated cell, depolarisation has to occur along the whole cell

Function of synapses

• Electrical impulse cannot cross junction

• Neurotransmitters send impulses between neurons for excitatory or inhibitory response

• Summation of sub-threshold impulses can occur

• New impulses can be initiated in several different neurons for multiple simultaneous responses

Structure of a synpase

• Synaptic knob

• Synaptic cleft

• Postsynaptic neuron

Role of acetylcholine

• Neurotransmitter in the parasympathetic system

• Rapidly broken down by enzymes

What happens in the presynaptic neuron when an action potential is transmitted between neurons

1. Wave of depolarisation travels down presynaptic neuron causing calcium channels to open

2. Vesicles move forward and fuse with presynaptic membrane

3. Exocytosis of neurotransmitter into synaptic cleft

Inhinitory synapse

• Neurotransmitter binds and opens Cl - channels and k channels

• Potassium moves out and chloride moves in

• Membrane becomes hyperpolarised so no action potential

Nicotine

• Mimics the effect of acetylcholine

• Binds to receptors and causes prevention of further action potentials

• Also causes release of dopamine

Lidocaine

• Blocks voltage gated Na ions

• Used as a local anaesthetic

• preventing production of an action potential

Cobra venom

• Binds to acetylcholine receptors

• Prevents transmission of impulses across synapses

• Muscles can’t contract

• Paralysis

• When reaches breathing muscles, death

Fovea

Region of the eye containing only cones, region of highest visual acuity

where are rod cells located

Evenly distributed Around periphery but NOT in central fovea

none in the blind spot where the optic nerve is

Where are cones located

Mainly in the central fovea

none on the blind spot where the optic nerve is

Why do rod cells not produce action potential in the dark

1. Na enters outer segment of rod cell via non-specific cation channels

Visual pigment in cones

Iodopsin

Where is the SAN located

Right atrium

Where is the AVN located

Inbetween right atrium and right ventricle

What stimulates the SAN

• The sympathetic system which releases Noradrenaline

• This also causes vasodilation which encourages blood flow to muscles.

Role of Baroreceptors in controlling heart rate

• During exercise vasodilation occurs

• This causes blood pressure to drop

• Response from the baroreceptors in the carotid artery reduces

• Causing the cardiac control centre to send signals to stimulate heart rate

Role of chemoreceptors in controlling heart rate

• Walls of the aorta and carotid arteries contain chemoreceptors

• As Co2 levels increase the pH drops and this is detected

• Chemoreceptors send signals to cardiac control centre to increase heart rate via the sympathetic nervous system

Adrenaline

• When stressed, sympathetic nervous system releases adrenaline

• Carried around the body in the blood stream and binds to numerous receptors including the SAN

How do podocytes work

• Located in the Bowmans capsule

• Has ‘pedicels’ which wrap around the capillary and has slits that small molecules can pass through

How is urea produced

• Amino acids are deamified to produce ammonia

• Ammonia is then converted to Urea in the ornithine cycle

How are the cells of the Bowmans capsule adapted for ultrafiltration

• Fenestrations between epithelial cells of capillaries

• Fluid can pass between and under folded membrane of podocytes

Outline the processes during selective reabsorption

• Glucose, amino acids, proteins, hormones taken up by active transport

• Water moves by osmosis

• Other ions diffuse down the conc gradient

Adaptations of proximal convoluted tube

• Covered with microvilli which greatly increases surface area

• Many mitochondria

• Blood flow maintains conc. gradient

Descending limb in the loop of henle

• Sodium and chloride ions enter via diffusion

• Water leaves as the limb is freely permeable to water

• At the bottom, the filtrate is at its most concentrated

Ascending limb of the loop of henle

• First section: Not permeable to water very permeable to sodium and chloride ions

• Sodium and chloride ions move out via diffusion

• Second section: Still not permeable to water, sodium and chloride ions actively pumped out

• GIving the medulla tissue a very low water potential

Distal convoluted tube

• Secretes waste chemicals like creatine into the filtrate

• Actively transports sodium chloride ions out if needed

• Helps control blood volume

Collecting duct

• Water potential of the plasma detected by osmoreceptors in the hypothalamus

• This controls how much ADH is released by the pituitary gland

• More ADH=More permeable

• ADH binds to receptors and triggers a series of membrane bound reactions

• This leads to the release of cAMP as the secondary messenger

• Vesicles containing water channels (aquaporins) move to the cell membrane

• Makes the membrane more permeable to water

How is a kangaroo rat adapted to its dry environment

• Spend most time in burrows

• Get water from food and metabolic reactions

• Very concentrated small amounts of urine

• Large proportion of juxtamedullary nephrons

• Long loops of henle

• HIgher number of unfolding s in the cell membranes of the epithelial cells lining the tubules giving a larger surface area

Endotherm Vs ectotherm

• Endotherm- Produces heat through metabolic reactions IE humans

• Ectotherms- Must rely on external environment for temperature

How do endotherms control body temperature

• Shivering - contraction of skeletal muscles stimulated by nerve impulses sent out by the hypothalamus, leading to an increase in temperature as heat is released

• Sweat glands - sweat production to decrease body temperature via evaporation from the skin surface

• Hairs on skin - lie flat to minimise insulation and increase heat loss, raised to provide insulation and decrease heat loss

• Arterioles - dilate to increase heat loss as blood flows closer to the skin, contract to reduce blood flow and therefore minimise heat loss

Cold environment adaptations

• Layers of fat

• Small extremeties

• Countercurrent flow systems in feet for example- as arteries lose heat, the veins are warmed as the run close to eachother

• hibernation

Hot environment adaptations

• Large extremeties with good blood flow to maximise heat loss IE elephant ears

• Tolerating temperature fluctuations IE camels

• Minimising water loss

• Countercurrent exchange system to keep the brain cool

Ecosystem

A life-supporting environment

Trophic level

The position in a food chain an organism occupies

Pyramid of numbers

• Simple

• Easy to measure

• Do not take into account the organisms size ie one tree would make the base small

Pyramid of biomass

• Takes into account an organisms size

• Biomass is difficult to obtain as the dry mass needs to be measured

Pyramid of energy

• Most accurate

• Very hard to measure as it requires burning dry organisms to see how much energy released

Why are there energy losses between trophic levels

• Some Is undigested

• SOme used by animal for respiration

• Some is lost as metabolic waste products

ACFOR scale

• Abundant

• Common

• Frequent

• Occasional

• Rare

  It is a subjective scale and no set definitions

Quadrat limitations

• Limitations to the area you can sample

• The randomness of the sample sites

• Decisions whether to include or exclude organisms partly covered by frame

Spearmans rank

Correlation between two factors IE between years passed on Surtsey and number of species

Student t test

See if two sets of data are significantly different from another for example mussel size between two beaches

Net primary productivity

• Energy stored as new plant tissue and used in respiration

• GPP-R

Gross primary productivity

• In plants is the rate which light from the sun catalysed the production of new plant material

• Very difficult to measure

Belt transect

• A combination of a line transect and a quadrat

Nitrogen fixing bacteria

• Converts Atmospheric Nitrogen into Ammoinum compounds

• Found in legume plant root nodules or just the soil

Nitrifying bacteria

• Turns Ammonium compounds into Nitrites and then nitrates

Denitrifying bacteria

• Converts nitrates to atmospheric nitrogen

Primary succesion

• When an area previously devoid of life is colonised

• Ie a new volcanic island

Succesion process

1. First colonised by a pioneer species which are adapted to live in harsh conditions

2. These species penetrate rock surface and break it down into grains.

3. As organisms die, they are decomposed adding humus, which leads to the formation of soil.

4. As more organisms decompose over time, the soil becomes richer in mineral content

5. Allowing larger more varied and productive plants to survive

6. Eventually a climax community is established which is the most productive community of organisms that the environment can support

Biotic factors affecting abundance and distribution of organisms

• Predation

• Reproductive partners

• Territory

• Parasites/disease

  Density may have an impact on this

Abiotic factors affecting abundance and distribution of species

• Light intensity

• Temperature

• Wind and water currents

• Water availability

• Oxygen availability

• Edaphic factors

Types of competition

• Interspecific competition- between individuals of the same species

• Intraspecific competition - Between individuals of different species

Evidence for climate change

• Co2 records

• Temperature records

• Pollen in peat bogs

• Dendrochronology - size of tree ring is affected by temperature