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What is starch?

A Polysaccharide.


Where is starch found?

In many parts of a plant in the form of small grains. Large amounts occur in seeds, storage organs.


What is starch made up of?

Alpha-glucose monosaccharides linked by glycosidic bonds formed in condensation reactions.

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How is a starch molecule made compact?

Unbranched chain wound into a tight coil.


What is the main role of starch?

Energy storage.


Why is starch suited for energy storage?

-INSOLUBLE- does not tend to draw water into cells by osmosis.

-Does not easily diffuse out of cells.

-COMPACT- a lot stored in a small space

-When HYDROLYSED forms alpha-glucose, which is easily transported and readily used in respiration.


Where is starch never found?

Animal cells.


How is glycogen different to starch?



Why is glycogen sometimes called "animal starch"?

Major carbohydrate storage product of animals.


How is glycogen stored in animals?

As small granules found mainly in the muscles and the liver.


Why is glycogen more readily hydrolysed than starch?

Shorter chains.


What is the main difference between cellulose and starch or glycogen?

Cellulose is made of monomers of beta-glucose.


How does beta-glucose affect the structure of cellulose?

In the beta-glucose units, the positions of the -H group and the -OH group on a single carbon atom are reversed. -OH above rather than below the ring. This means that to form glycosidic links, each beta-glucose molecule must be rotated by 180 degrees compared to its neighbour. Result: -CH2OH group on each beta-glucose molecule alternates between being above and below the chain.

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What shape does cellulose chains make?

Straight chains, unbranched.

These run parallel to one another, allowing hydrogen bonds to form cross linkages between adjacent chains.

Amount of hydrogen bonds makes cellulose very strong.


What are microfibrils?

Groups of cellulose molecules.


What are fibres?

Parallel groups of microfibrils (Groups of cellulose molecules)


What is cellulose used for and why is it good?

Major component in pant cell walls. Provides rigidity to plant cells. Prevents cell from bursting as water enters by osmosis. Exerts inwards pressure that stops any further influx of water. As a result, living plant cells are turgid and push against one another


Describe the structure of haemoglobin.

PRIMARY- Consists of 4 polypeptide chains.

SECONDARY- in which each of these polypeptides chains is coiled into a helix

TERTIARY STRUCTURE- in which each polypeptide chain is folded into a precise shape-


QUATERNARY STRUCTURE- all for polypeptides are linked togehter to form an almost spherical molecule. Each polypeptide is associated with a HAEM group- contains ferrous (Fe2+) ion. Each Fe2+ ion can combine with a single oxygen molecule, making a total of four O2 molecules that can be carried by a single haemoglobin molecule in humans.


What is the role of haemoglobin?

To transport oxygen


To be efficient at transporting oxygen haemoglobin must...

-Readily associate with O2 at surface where gass exchange takes place.

-Readily dissociate from oxygen at those tissues requiring it.


What property of haemoglobin allows it to readily associate and dissociate with oxygen?

it changes its affinity for oxygen under different conditions.


How does haemoglobin change its affinity for oxygen?

Its shape change in the presence of certain substances, e.g. CO2. In the presence of CO2, the new shape of the haemoglobin binds MORE LOOSELY to oxygen. As a result haemoglobin releases its oxygen. i.e. in tissues due to higher levels of CO2


Describe the oxygen conc., CO2 conc., the affinity of haemoglobin for oxygen and the result of all of these at the gas exchange surface.

O2 conc.- HIGH

CO2 conc. - LOW

Affinity of haemoglobin for oxygen- HIGH

RESULT: Oxygen attached


Describe the oxygen conc., CO2 conc., the affinity of haemoglobin for oxygen and the result of all of these at the respiring tissues.

O2 conc.- LOW CO2 conc.- HIGH Affinity of haemoglobin for O2- LOW RESULT: Oxygen released


Describe what haemoglobins with a high affinity for oxygen do.

Take up oxygen more easily but release it less readily


Describe what haemoglobins with a low affinity for oxygen do.

Take up oxygen less easily but release it more readily.


Describe an organism that could have haemoglobin with a high affinity for oxygen.

An organism living in an environment with little O2. This is provided that the organism's metabolic rate is not very high so that the fact that this form of haemoglobin doesn't release O2 as readily to the tissues will not be a problem.


Describe and organism that could have haemoglobin with a low affinity for oxygen.

High metabolic rate- need to release O2 more readily to tissues. Provided there is plenty of O2 in the organisms environment.


Why do different haemoglobins have different affinities for oxygen?

Different haemoglobin molecules have slightly different sequences of amino acids and therefore slightly different shapes. So, depending on the shape, different haemoglobin range from a low affinity for oxygen and a high affinity for oxygen.



The process by which haemoglobin combines with oxygen. e.g. in humans- in lungs



The process by which haemoglobin releases its oxygen. e.g. in humans- in tissues



The amount of gas that is present in a mixture of gases is measured by the pressure it contributes to the total pressure of the gas mixture. WRITTEN AS pO2. MEASURED IN kPa


Describe the relationship between oxygen concentration and the uptake of the oxygen by haemoglobin. (OXYGEN DISSOCIATION CURVE)

At very low conc. of oxygen, the four polypeptides of the haemoglobin molecule are closely united, and so it is difficult to absorb the first oxygen molecule. HOWEVER Once loaded, this oxygen molecule causes the polypeptides to load the remaining three oxygen molecules very easily. THE GRAPH OF THIS RELATIONSHIP IS KNOWN AS THE OXYGEN DISSOCIATION CURVE.


What is the impact of a very small decrease in partial pressure of oxygen?

Leads to a lot of oxygen becoming dissociated from the haemoglobin.


Why does O2 dissociation curve tail off at very high O2 conc.

Because the haemoglobin is almost saturated with O2


What does the position of an oxygen dissociation curve tell you? (further to left/right)

-The further to the left the curve, the greater is the affinity of haemoglobin for oxygen (takes up more readily, releases less readily.

-The further to the right the curve, the lower the affinity of haemoglobin for oxygen (take up less readily, releases more.


Describe what occurs at the gas exchange surface in terms of haemoglobin and CO2.

The level of CO2 is low because it diffuse across the exchange surface and is expelled from the organism. The affinity of haemoglobin for oxygen is increased, which, coupled with the high conc. of oxygen in the lungs, means oxygen is readily loaded by haemoglobin. Reduced CO2 level has shifted O2 dissociation curve left.


Describe what occurs at the respiring tissues in terms of haemoglobin and CO2 conc.

e.g.muscles. The level of CO2 is high. The affinity of haemoglobin for oxygen is reduced, which, coupled with the low conc. of O2 in the muscles, means that oxygen is readily unloaded from the haemoglobin into the muscle cells. The increased CO2 level has shifted the O2 dissociation curve to the right.


Why exactly does a greater conc. CO2 cause haemoglobin to release O2 more readily?

Dissolved CO2 is acidic and the low pH causes haemoglobin to change shape.


Describe the process of loading, transporting and unloading oxygen.

-At gas exchange surface CO2 is constantly being removed.

-The pH is raised due to low level of CO2

-The higher pH changes the shape of haemoglobin into one that enables it to load O2 readily.

-This shape also increases the affinity of haemoglobin for oxygen, so it is not released while being transported in the blood to the tissues.

-In the tissues, CO2 is produced by respiring cells.

-CO2 is acidic in solution, so pH of blood within tissues is lowered.

-The lower pH changes the shape of haemoglobin into one with a lower affinity for O2.

-Haemoglobin releases its oxygen into respiring tissues.


The more active a tissue, the more oxygen that is unloaded. How does this work?

The higher the rate of respiration---> The more CO2 the tissues produce----> The lower the pH -----> The greater the haemoglobin changes shape ----> The more readily O2 is unloaded ----> The more O2 is available for respiration.


What happens when haemoglobin reaches a tissue with a low respiring rate?

One of the four O2 molecules usually released. The blood returning to lungs will therefore contain haemoglobin that is still 75% saturated with O2.


What is the function of a palisade leaf cell?



What are the features of a palisade leaf cell that makes it suited to photosynthesis?

-long, thin cells that form a continuous layer to absorb sunlight.

-numerous chloroplasts that arrange themselves in the best positions to collect the maximum amount of light

-a large vacuole that pushes the cytoplasm and chloroplasts to edge of cell. 

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The organelles that carry out photosynthesis.


What are the three main features of chloroplasts? Explain.

-THE CHLOROPLAST ENVELOPE is a double plasma membrane that surrounds the organelle. It is highly selective in what it allows to enter and leave the chloroplast.

-THE GRANA are stacks of up to 100 disc like structures called THYKALOIDS. Within thykaloids is the photosynthetic pigment called CHLOROPHYLL. Some thykaloids have tubular extensions that join up with thykaloids in adjacent grana. THE GRANA ARE WHERE THE FIRST STAGE OF PHOTOSYNTHESIS OCCURS.

-THE STROMA is a fluid-filled matrix where the second stage of photosynthesis occurs. A number of other structure within stroma. (SEE DIAGRAM)

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In what 3 ways are chloroplasts adapted to carrying out photosynthesis?

-The granal membranes provide a large surface area for the attachment of chlorophyll, electron carriers and enzymes that carry out the first stage of photosynthesis. These chemicals are attached to the membrane in a highly ordered fashion.

-The fluid of the stroma possesses all the enzymes needed to carry out the second stage of photosynthesis.

-Chloroplasts contain both DNA and ribosomes so they can quickly and easily manufacture some of the proteins needed for photosynthesis.


Describe the cell wall of a plant cell.

Consists of microfibrils of the polysaccharide cellulose, embedded in a matrix. Cellulose microfibrils have considerable strength and so contribute to overall strength of cell wall.


What are 2 features of cell walls?

-Consist of a number of polysaccharides, such as cellulose

-There is a thin layer, called the middle lamella, which marks the boundary between adjacent cell walls and cements adjacent cells together.


What are the 3 functions of a cellulose cell wall?

-To provide mechanical strength in order to prevent the cell bursting under pressure created by the osmostic entry of water.

-To give mechanical strength to the cell as a whole.

-To allow water to pass along it and so contribute to the movement of water through the plant.


What are the key differences between plant(4) and animal cells(4)?


-Only a cell surface membrane surrounds cell.

-Chloroplasts never present.

-If vacuoles are present they are small and scattered throughout cell.

-Glycogen granules are used for storage.


-Cellulose cell wall surrounds the cell as well as a cell surface membrane.

-Chloroplasts are present in large numbers in most cells.

-Normally have large, single, central vacuole filled with cell sap.

-Starch grains are used for storage.



The structures through which the vast majority of water is transported.

Thick cell walls.

As they mature, their walls incorporate a substance called lignin and the cells die.

The end walls break down, which allows the cells to form a continuous tube.

Lignin often forms spirals around the vessel.



Each root hair is an extension of a root epidermal cell.

Root hairs are the exchange surfaces in plants that are responsible for the absorption of water and mineral ions.

These root hairs remain functional for a few weeks before dying back, to be replaced by others nearer the growing tip.


How do root hairs absorb water?

BY osmosis. the soil solution surrounds the particles that make up soil. It contains a very low conc. of mineral ions dessolved in water. The root hairs, however have a high conc. of mineral ions and sugars within their vacuoles and cytoplasm. Because root hairs are in direct contact with the soil solution, water moves by osmosis from soil solution into root hair cells.


How does the root hair cell take up mineral ions?

Conc. of mineral inside root hair cell is normally higher than that in soil solution. The uptake of mineral ions is therefore AGAINST A CONCENTRATION GRADIENT. REQUIRES ACTIVE TRANSPORT. Uses special carrier proteins that use ATP. This provides energy to transport particular ions from the oil solution to root hair cytoplasm and vacuole.