Unit 2, Topic 4 notes

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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
Vacuolar membrane Stretchy membrane around Protects the vacuole and
(tonoplast) vacuole isolate it from harmful
substances. The tonoplast
membrane controls ionic
movement in and around
the cell. Water flowing in
and out of the vacuole is
regulated by the tonoplast
Chloroplast Double membrane structure, Site of photosynthesis
inner layer forms lamellae
(thylakoids) which are
arranged in flattened circular
piles (Grana) where
chlorophyll is located.
Contains stroma (small starch
grains). type of plastids with
an aqueous matrix
Smooth endoplasmic System of interconnected Site of lipid and steroid (e.g.
reticulum membrane-bound, flattened reproductive
sacs but doesn't have any hormones)production
attached ribosomes
Pit Regions of the cell wall where Plasmodesmata often
the wall is very thin. They're located in pits = aids
arranged in pairs ­ the pit in one movement of substances
cell is lined up with the pit in the between cells
adjacent cell
Plasmodesma Narrow fluid-filled channels Aids movement of
that cross the cell walls, substances between cells
making the cytoplasm of one
cell continuous with the
cytoplasm of the next

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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
to the outer surface.…read more

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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 the cell.
Amyloplast (containing Colourless plastids in which Responsible for the synthesis
starch grains) starch grains are stored and storage of starch
granules
Can convert this starch back
into sugar when the plant
needs energy.…read more

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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 is stored as glycogen
in animal cells
Only plants have a cell wall
(3) Compare the structure and function of the polysaccharides starch and
cellulose including the role of hydrogen bonds between -glucose molecules
in…read more

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H bonds in the microfibril produces
a strong structure.…read more

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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 cells with thick
cell walls.
Forms columns of cells acting as tubes for the transport of water and mineral ions.…read more

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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 out of the xylem and
5.…read more

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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 strength
Lignin is laid down in spirals or in rings in xylem cell walls
The taller a plant needs to grow, the greater the proportion of its stem that becomes
lignified
The living part of…read more

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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 are carbon neutral, biodegradable and can be
reproduced
However, there are problems with plant-based products and sustainability cannot be
guaranteed as we need to consider the source of the plant product, the energy used and
pollution created during the production and transport of the product.…read more

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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 ­ dissolved substances can be transported around plants through
the xylem and phloem.…read more

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