Flashcards in 10.3 Starch, Glycogen And Cellulose Deck (37):
Starch is a mono/di/polysaccharide?
In the plant, in what form is starch found?
As starch gains.
Where do large amounts of starch occur?
Seeds and storage organs, such a potato tubers.
What is the major energy source in most diets?
What is starch made up of and what are they linked by?
Chains of alpha glucose monosaccharides linked by glycosidic bonds.
How are glycosidic bonds formed?
By condensation reactions.
What is the main role of starch?
Why is starch suited to energy storage?
- it is insoluble and doesn't draw water into the cells by osmosis
- being insoluble, it does not easily diffuse out of cells
- it is compact, so a lot of it can be stored in a small space
- when hydrolysed it forms alpha-glucose, which is both easily transported and readily used in respiration.
Starch is NEVER found in...
Glycogen has a similar structure to ...
Starch ( but has shorter chains and is more highly branched).
Glycogen is sometimes called 'animal starch' because...
It is the major carbohydrate storage product of animals.
How is glycogen stored?
In animals it is stored as small granules mainly in the muscles and liver.
Glycogens structure suits it's functions for the same...
Reasons as starch but it is even more readily hydrolysed to alpha glucose because it is made up of smaller chains.
Glycogen is NEVER...
Found in plant cells.
How does cellulose differ from starch and glycogen?
It is made of monomers of beta glucose rather than alpha glucose.
The beta glucose composition of cellulose produces fundamental differences in the structure and function of this polysaccharide. How?
In the beta glucose units, the positions of the -H group and the -OH group are reversed. This means that to form glycosidic links, each beta glucose molecule must be rotated 180 degrees compared to its neighbour. The result is that the CH2OH group on the beta glucose alternates between being above and below the chain.
What is the shape of cellulose?
Rather than forming a coiled chain like starch, cellulose has straight unbranched chains. These run parallel to one another, allowing hydrogen bonds to form cross-linkages between adjacent chains.
How do the cross-linking hydrogen bonds contribute to the strengthening of cellulose?
While each individual hydrogen bond adds very little to the strength of the molecule, the sheer overall number of them makes a considerable contribution to the strength of cellulose. This makes it a valuable structural material.
The cellulose molecules are grouped together to form...
Microfibrils which are arranged in parallel groups called fibres.
What is cellulose a major component of?
Plant cell walls. It provides rigidity to the plant cell.
Cellulose plays a role during osmosis...
The cell wall exerts an inward pressure that stops any further influx of water.
Cellulose is especially important for photosynthesis. Why?
It indirectly maintains stems and leaves in a turgid state so that they can provide the maximum surface area for photosynthesis.
Name a typical plant cell.
What is the function of a palisade cell?
To carry out photosynthesis.
What is the infrastructure of a palisade cell?
- 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 the edge of the cell.
What is the function of chloroplasts?
They carry out photosynthesis.
Name the main features of a chloroplast.
The chloroplast envelope - double, selective in what enters and leaves.
The grana - staks of up to 100 disc like structures called thylakoids. They contain the photosynthetic pigment - chlorophyll. Some thylakoids have tubular extensions that join up with thylakoids in adjacent grana. The grana are where the first stage of photosynthesis takes place.
The stroma: fluid-filled matrix where the second stage of photosynthesis takes place. They can contain starch grains.
How are chloroplasts adapted to their function?
- The gradual members provide a large surface area for the attachment of chlorophyll, electron carriers and enzymes that carry out the first stage of photosynthesis. The 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 DNA and ribosomes so they can quickly and easily manufacture some of the proteins needed for photosynthesis.
List the features of cell walls.
- They consist of a number of polysaccharides, such as cellulose
- there is a thin layer, called middle lamella, which marks the boundary between adjacent cell walls and cements adjacent cells together.
What are the functions of the cellulose cell wall?
To provide mechanical strength in order to prevent the cell bursting under the pressure created by the osmotic entry of water.
To give mechanical strength to the plant as a whole
To allow water to pass along it and so contribute to the movement of water through the plant.
Root hair cells absorb...
Water from the soil. (By osmosis).
Root hair cells absorb mineral ions by...
Active transport. (Carrier proteins)
Give the differences between plant and animal cells.
Plant: cellulose cell wall and cell-surface membrane
Animal: only a cell-surface membrane
Plant: chloroplasts present in large numbers
Animal: no chloroplasts
Plant: normally have a large, single, central vacuole filled with cell-sap
Animal: If vacuoles are present they are small and scattered throughout the cell
Plant: starch gains used for storage
Animal: glycogen granules used for storage
Xylem vessels have what kind of cell walls?
Thick cell walls.
As they mature which substance do xylem walls incorporate into their cells?