10.3 Starch, Glycogen And Cellulose

Question 0

In the plant, in what form is starch found?

Answer 0

As starch gains.

Question 1

Starch is a mono/di/polysaccharide?

Answer 1

Polysaccharide.

Question 2

Where do large amounts of starch occur?

Answer 2

Seeds and storage organs, such a potato tubers.

Question 3

What is the major energy source in most diets?

Answer 3

Starch

Question 4

What is starch made up of and what are they linked by?

Answer 4

Chains of alpha glucose monosaccharides linked by glycosidic bonds.

Question 5

How are glycosidic bonds formed?

Answer 5

By condensation reactions.

Question 6

What is the main role of starch?

Answer 6

Energy storage.

Question 7

Why is starch suited to energy storage?

Answer 7

• 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.

Question 8

Starch is NEVER found in…

Answer 8

Animal cells.

Question 9

Glycogen has a similar structure to …

Answer 9

Starch ( but has shorter chains and is more highly branched).

Question 10

Glycogen is sometimes called ‘animal starch’ because…

Answer 10

It is the major carbohydrate storage product of animals.

Question 11

How is glycogen stored?

Answer 11

In animals it is stored as small granules mainly in the muscles and liver.

Question 12

Glycogens structure suits it’s functions for the same…

Answer 12

Reasons as starch but it is even more readily hydrolysed to alpha glucose because it is made up of smaller chains.

Question 13

Glycogen is NEVER…

Answer 13

Found in plant cells.

Question 14

How does cellulose differ from starch and glycogen?

Answer 14

It is made of monomers of beta glucose rather than alpha glucose.

Question 15

The beta glucose composition of cellulose produces fundamental differences in the structure and function of this polysaccharide. How?

Answer 15

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.

Question 16

What is the shape of cellulose?

Answer 16

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.

Question 17

How do the cross-linking hydrogen bonds contribute to the strengthening of cellulose?

Answer 17

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.

Question 18

The cellulose molecules are grouped together to form…

Answer 18

Microfibrils which are arranged in parallel groups called fibres.

Question 19

What is cellulose a major component of?

Answer 19

Plant cell walls. It provides rigidity to the plant cell.

Question 20

Cellulose plays a role during osmosis…

Answer 20

The cell wall exerts an inward pressure that stops any further influx of water.

Question 21

Cellulose is especially important for photosynthesis. Why?

Answer 21

It indirectly maintains stems and leaves in a turgid state so that they can provide the maximum surface area for photosynthesis.

Question 22

Name a typical plant cell.

Answer 22

Palisade cell

Question 23

What is the function of a palisade cell?

Answer 23

To carry out photosynthesis.

Question 24

What is the infrastructure of a palisade cell?

Answer 24

- 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.

Question 25

What is the function of chloroplasts?

Answer 25

They carry out photosynthesis.

Question 26

Name the main features of a chloroplast.

Answer 26

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.

Question 27

How are chloroplasts adapted to their function?

Answer 27

- 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.

Question 28

List the features of cell walls.

Answer 28

- 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.

Question 29

What are the functions of the cellulose cell wall?

Answer 29

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.

Question 30

Root hair cells absorb...

Answer 30

Water from the soil. (By osmosis).

Question 31

Root hair cells absorb mineral ions by...

Answer 31

Active transport. (Carrier proteins)

Question 32

Give the differences between plant and animal cells.

Answer 32

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

Question 33

Xylem transport...

Answer 33

Water

Question 34

Xylem vessels have what kind of cell walls?

Answer 34

Thick cell walls.

Question 35

As they mature which substance do xylem walls incorporate into their cells?

Answer 35

Lignin

Question 36

What happens when lignin is incorporated into the walls of xylem vessels?

Answer 36

The cells die and the end walls break down which allows the cells to form a continuous tube. Lignin often forms rings or spirals around the vessel.