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Topic 4
((2) Compare the ultrastructure of plant cells (cell wall,
chloroplasts,amyloplasts, vacuole, tonoplast, plasmodesmata, pits and middle
lamella) with that of animal cells.)

The ultrastructure of a plant cell

Structure function

Ribosomes Made of RNA and protein, Site of protein synthesis
found free in cytoplasm or
attached the RER…

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Middle lamella Outermost layer of the cell, Acts as an adhesive, sticking
gel-like layer of calcium adjacent plant cells together.
pectate It gives the plant stability
Rough endoplasmic System of interconnected Site of protein synthesis,
reticulum membrane-bound, flattened proteins made in ribosomes
sacs with ribosomes attached and are transported through…

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Separates interior of the
cell from the outer
environment.
It enables transport of
substances and
information from the cell
insides to the exterior
and vice versa.
Helps in
osmotic-regulation.
Prevents water loss.
It prevents the cell from
breaking due to
pressure.
Aids in diffusion of gases
in and out of…

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Comparison to an animal cell:

They both have:
Cytoplasm plasma membrane
Nucleus
Mitochondria
Smooth and rough endoplasmic reticulum
Golgi apparatus
Ribosomes
Lysosomes

Differences are:
Only animal cells have centrioles
Only plant cells have a vacuole
Only plant cells have chloroplasts
Carbohydrates stored in plants as starch in amyloplasts while it…

Page 5

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with glycosidic bonds, but together the large number of H bonds in the microfibril produces
a strong structure.

Microfibrils are wound in helical arrangement around the cell and stuck together with a
`polysaccharide glue'

Glue -> short, branched polysaccharides ( hemicelluloses and pectins ) ­ these bind to the
surface…

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Phloem: transports sugars made by photosynthesis in the leaves up and down the plant

Cambium: layer of actively dividing cells between xylem and phloem tissues that is
responsible for the secondary growth of stems and roots

Xylem:

Carries water and inorganic ions up through the stem, made up of large…

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Pits allow movement between vessels




Water moves up xylem by transpiration (1.
water vapour diffuses through the stoma down the diffusion gradient, 2. water
evaporates from the surfaces of cells lining the substomatal cavity, 3. water replaced by
means of CAPILLARY ACTION within the cell walls, 4. water is drawn…

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Movement of water through xylem provides a mass flow system for the transport of
inorganic ions which are absorbed by roots and needed throughout the plant




Xylem and sclerenchyma for support:

Lignin is found in xylem and sclerenchyma and makes cell walls stiffer and give the
plant much greater tensile…

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made by the fermentation of sugars from wheat, sugar beet, potatoes or agricultural waste
= more sustainable = biodegradable

Use of oil-based plastics and fuels are not sustainable because burning fossil fuels releases
carbon dioxide, oil reserves will run out and plastics generate non-biodegradable waste

Plant-based products sustainable as they…

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Water:

Cohesion and surface tension ­ H bonds between water molecules results in strong
cohesive forces between water molecules that keep the water together as a
continuous column in xylem vessels. Surface tension at water surfaces also caused by
cohesive forces which causes the surface layer to contract.
Solvent properties…

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