Unit 2 AS Biology Edexcel

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  • Created by: Chelsey
  • Created on: 21-12-12 15:08

Plant cell structure

Cell wall-

Rigid structure that surrounds plant cells, mainly made of cellulose.

Supports plant cells 

Middle lamella-

outermost layer

acts an adhesive sticking adjacent cells together. It gives stability.


channels in cell walls that link adjacent cells

allows transport of substances and communication between cells 

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plant cell structure


regions of cell wall where very thin, arranged in pairs

allows transport of substances between cells


flattened, double membrane, has thylakoid membranes, stacked to form grana, grana linked by lamellae.

Site of photosynthesis


membrane bound organellse that contains starch

storage of starch grains, convert starch to glycogen for release when plant needs it

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Plant cell structure

Vacuole and tonoplast-

vacuole is a compartment surrounded by a membranen called the tonoplast.

vacuole contains cells sap= water, enzymes, minerals and waste products.

Vacuole keeps cells trugid- stops plants wilting, invovled in breakdown and isolation of unwanted chemicals in the cell. tonoplast controls what enters and leaves the vacuole.

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Xylem vessels

Function: to transport water and mineral ions up the plant, and provide support

Structure: long, tube-like structures formed from dead cells, found in bundles. Hollow lumen, no end walls. 

This makes an uninterrupted tube, allowing water and mineral ions to pass up through the middle easily.

Walls are thickened by lignin, which helps support the plant.

water and mineral ions move into and out of the vessels through pits in the walls where theres no lignin.

They are found throughout the plant but particularly around the centre of the stem.

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Sclerenchyma fibres

Function: provide support

structure: bundles of dead cells, hollow lumen and no end walls, walls strengthened by lignin, found throughout stems of plants but particularly around the outer edge.

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The difference between starch and cellulose

Starch- main energy storage material in plants, store excess glucose as starch

made of a-glucose molecules, starch is a mixture of:

amylose- long, unbranched chain. coiled structure due to bonds, compact, good for storafe, more into small space

amylopectin- long, branched chain. side branches allow enzymes that break down the molecule to get at the bonds easily. glucose released quickly

starch is insoluble in water, doesnt cause water to enter cells by osmosis. good forb storage.

Ceullulose-  major component of cell walls in plants

long, unbranched chains of b-glucose, joined by glycosidic bonds, bonds are straight so cellulose chains are straight. chains are linked by hydrogen bonds to form microfibrils, which provide structural support.

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Plant fibres

made up of long tubes of plant cells 

They are very strong for two reasons:

The arrangement of cellulose microfibrils in the cell wall

net-like arrangement

The secondary thickening of cell walls

when some structural plant cells stop growing, they produce a secondary cell wall in between the cell membrane and the normal cell wall.

This is thicker than the normal cell wall and usually has more lignin.

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