OCR Biology F214 Communication, Homeostasis and Energy Friday 22 June 2012

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define homeostasis and give example of negative feedback(5)

Homeostasis is the maintenance of a constant internal environment despite external changes.

An example is the hormone oxytocin which is used during pregnancy to dilate the cervix to allow a baby to get through

Discuss factors which affect heart rate (8)

Reply 101

otrivine

Original post by rf229

really good yes full marks

Increase exercise increases heart rate and hormone adrenaline increases the heart rate and during this horonal and nervous system carry signals to heart. The heart is controlled by the medulla oblongata of the brain in cardiovascular centre. SAN intiates wave of excitation and blood travels to AVN then to purkyne then pushed out of blood when ventricles contract. Increase co2 level is detected by chemoreceptors which send signal to the heart that more oxygen has to be transported. Also, increasing exercise increases heart rate and is detected by stretch receptors and so indicaties more oxygen has to be transported around the body so that organs can reciveve a good supply of oxygen to carry out metabolic processes

Reply 102

rf229

Original post by otrivine

Sorry didn't see this...
Well done, I would give that full marks

Outline non-cyclic photophosphorylation (5)

Reply 103

otrivine

Original post by rf229

Sorry didn't see this...
Well done, I would give that full marks

Outline non-cyclic photophosphorylation (5)

did not revise that doing it this evening :wink:

sorry can u give me questions from chapter 1 and 2 :wink:

Describe how insulin is controlled(5)

Reply 104

undertaker1

guys, could someone please explain photosynthetic pigments, those funnels, and photosystems please?

Reply 105

Robpattinsonxxx

Original post by rf229

So we got...
1. Vagus nerve which sends impulses to the sinoatrial node to decrease heart rate.
2. Accelerator nerve which sends impulses to sinoatrial node to increase heart rate.
3. Release of adrenaline from the adrenal medulla which increases heart rate to prepare the body for activity.
4. The build up of co2 inside the body and decreased oxygen levels increase heart rate to bring in more o2 and release co2.
5. Movement of limbs detected by stretch receptors in muscles send impulses to cardiovascular centre, increasing heart rate to obtain more o2.
6. Increased blood pressure monitored by stretch receptors in walls of carotid sinus. The stretch receptors send signals to cardiovascular centre to decrease heart rate.

Reply 106

Robpattinsonxxx

Original post by undertaker1

guys, could someone please explain photosynthetic pigments, those funnels, and photosystems please?

Photosynthetic pigments e.g chlorophyll a are molecules that absorb or reflect light energy of a range of wavelengths. They convert the light energy to chemical energy.

Photosystems are arranged in funnel-shaped structures and are a cluster light harvesting photosynthetic pigments and protein molecules in the thylakoid membranes. THey channel the light energy to chlorophyll molecules. The primary pigment reaction centre is chlorophyll a and accessory pigments are molecules of chlorophyll b and carotenoids. This arrangement allow maximum absorption of light energy.

Reply 107

Robpattinsonxxx

Original post by rf229

Sorry didn't see this...
Well done, I would give that full marks

Outline non-cyclic photophosphorylation (5)

Basically consists of a z scheme. Light is absorbed by PSI, causing two electrons to be released and be captured by electron acceptors. THey are then passed down electron carriers, releasing energy as they do which is used to produce ATP.

At PSII, there is the photolysis of water. 2H2O-->4H++4e-+O2. The protons from the photolysis of water and electrons from PSI are combined with NADP to produce NADP reduced which goes to the electron transport chain to produce ATP molecules. Light is absorbed by PSII causing two electrons to be released. These electrons replace the electrons lost by PSI. The electrons from the photolysis of water replace those lost by PSII.

O2 is removed as a waste product. The products of non cyclic photophosphorylation are o2, reduced NADP and ATP.

Reply 108

Robpattinsonxxx

Original post by otrivine

did not revise that doing it this evening :wink:

sorry can u give me questions from chapter 1 and 2 :wink:

Describe how insulin is controlled(5)

The potassium ion channels are open so potassium ions diffuse out of the cell, making the inside of the cell more negative.

Glucose diffuses into the cell through glucose transporter proteins, are phosphorylated and metabolised to produce ATP.

The ATP causes potassium channels to close and this change in potential difference across the membrane causes calcium channels to open. Calcium ions enter the cell.

This causes vesicles containing insulin to move and fuse with the plasma membrane, releasing insulin by exocytosis.

Reply 109

otrivine

Original post by Robpattinsonxxx

good but give me some questions as well come on man or girl :biggrin:

Reply 110

Robpattinsonxxx

Original post by otrivine

good but give me some questions as well come on man or girl :biggrin:

Girl ok

right...

Outline the roles of synapses in the nervous system. :smile:

Reply 111

otrivine

Original post by Robpattinsonxxx

Girl ok

right...

Outline the roles of synapses in the nervous system. :smile:

sorry

- one direction
-impulses are transmitted across synapses
- nerve impulses travels along neurone
- unwanted signals are filtered
-ammulcation (sorry spelling )where low level of signals are amplified
-

Reply 112

Robpattinsonxxx

Original post by otrivine

sorry

Yep they are all right. So basically to connect two neurones together so signals can be passed between them, one direction (e.g. as presynaptic neurone only contains acetylcholine vesicles), filter out low level signals as they are unlikely topass across the synapse as A LOT of vesicles have to be released and yeah acclimatisation where the NS does not respond to a stimulus to avoid overstimulation and damage of the effector. It's where a synapse runs out of vesicles.

Also some others for you:
* Several presynaptic neurones may converge to one postsynaptic neurone so allow signals from different parts of the NS to create the same response.
* One presynaptic neurone may converge to several post synaptic neurones so allow one signal to be transported to several parts of the NS.
* Low level signals can be amplified by summation.

Reply 113

Robpattinsonxxx

Next question:

Describe how the structure of chloroplasts AND mitochondria enable the organelles to carry out their function. Try describe 5 points for each :smile:

Reply 114

otrivine

Original post by Robpattinsonxxx

Next question:

Describe how the structure of chloroplasts AND mitochondria enable the organelles to carry out their function. Try describe 5 points for each :smile:

chloroplasts - have a shape of 2-10um long , consits of many thylakoids and therefore more grana so for light independent stage to occur and to hold enzymes,electron carriers, ATPsynthaise.Also, the photosynthetic pigments are arranged in a special structure called photosystems to enable maximum absorption of light. Also, chloroplasts have a nuclear envelope which separates the inside and outside cell
Mitochondria has cristae which proves a large surface area for enzymes, also, has a matrix filled fluid to carry out processes such as krebs cycle and link reactions. Also, are sausage shaped ,

Reply 115

Robpattinsonxxx

Original post by otrivine

ALso, for chloroplasts: Starch grains in stroma so plants can store carbohydrates, ribosomes and a circular strand of DNA. Inner membrane has transport proteins. Grana have large sa! Stroma contains enzymes for the calvin cycle. Grana in close contact with stroma so products from LDR can pass into the stroma for the LIR.

Also for mitrochondria: Matrix contains enzymes for LR and KC. Outer membrane has channel/carrier proteins to enable molecules like pyruvate to enter the matrix from the cytoplasm. Electron carriers and ATP synthase enzymes embeded in the inner membrane.

Well done :smile:

Reply 116

otrivine

Original post by Robpattinsonxxx

thanks

and will that get me full marks what i wrote cause i wrote more that 5 points ??

ok
Describe what happens to increase glucose conc? (4)

Reply 117

Robpattinsonxxx

Original post by otrivine

Remember to expland on your thylakoids and grana. Say they consist as many to provide a large surface area. As you haven't really compared structure and function for that. State where the enzymes, electron carriers and ATP synthase enzymes are. You would def get a mark for your photosystems point. Must expand on your last point about the envelope.

You would get a mark about the cristae. Not one about the shape as i don't know the advantage of that? Also mention what the matrix has e.g. enzymes to carry out the KC and LR.

I know that you know what you mean but i would be abit more clearer in your answers and expand your points more :smile:

Reply 118

otrivine

Original post by Robpattinsonxxx

thanks

so how many marks cause usally ocr marks for key words?

Reply 119

Robpattinsonxxx

Original post by otrivine

thanks

and will that get me full marks what i wrote cause i wrote more that 5 points ??

ok
Describe what happens to increase glucose conc? (4)

* Decrease in blood glucose concentration detected by a cells in the pancreas.

* A cells respond by secreting more glucagon and less insulin into the blood.

* Hepatocytes possess the receptor for glucagon and respond by initiating glycogenolysis.

* There is also increase in production of glucose by gluconeogenesis.

* This increases blood glucose concentration.