AQA AS Biology Unit 2- Plants

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It is a typical plant cell. Its function is to carry out photosynthesis. They
are adapted to carry out its function in many ways:-
Long, thin cells that form
a continuous layer to
absorb sunlight
Contains lots of
chloroplast that arrange
in the best position to
collect maximum amount
of sunlight
A large vacuole that
pushes the cytoplasm and
the chloroplasts to the
edge of the cell
They vary in shape and size and disc shaped. The main features are:-
THE CHLOROPLAST ENVELOPE- it is a double plasma membrane that
surrounds the organelle. It is very selective in what it allows to enter and leave
The GRANA are stacks of up to 100 disc-like structures called
THYLAKOIDS. Within the thylakoids is the photosynthetic pigment called
chlorophyll. Some thylakoids are joined to adjacent grana by having tubular
STROMA- it is a fluid filled matrix which contains a number of other structures
How chloroplasts are adapted to carry out its function of
harvesting sunlight and carrying out photosynthesis:-

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Granal membranes provide a large surface area for the attachment of
chlorophyll, electron carriers and enzymes that carry out first stage of
Fluid of stroma possesses all the enzymes needed to carry out the second
stage of photosynthesis
Chloroplast contains both DNA and ribosomes so they can quickly and easily
manufacture some of the proteins needed for photosynthesis.
Cell wall consists of micro fibrils of the polysaccharide cellulose, embedded in a
matrix.…read more

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When a "young" plant cell is formed, it is surrounded by a primary cell wall
composed largely of cellulose. The cell wall is secreted by the protoplast it
encloses. This primary cell wall consists of cellulose fibres arranged at random
within the matrix such that the primary wall is highly porous.…read more

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Root hair cells
Root hair cell is an extension of a root epidermal cell. They are exchange surfaces
in plants that are responsible for intake of water and mineral ions. Root hairs
absorb water by the process of osmosis. The concentration of ions inside the root
hair cell is normally greater than that in the soil. The uptake of mineral ions is
therefore against the concentration gradient, so it requires active transport. This
is achieved using carrier proteins that use ATP.…read more

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Starch, glycogen and cellulose
Starch is a polysaccharide that is found in many parts of plants such as small
grains, seeds and storage organs. It is made up of glucose
monosaccharide linked by glycosidic bonds that are formed by
condensation reaction. The unbranched chain is wound into a tight coil that
makes the molecule very compact.…read more

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The cellulose molecules are grouped together t form microfibrils whcih in turn are
arranged in parallel groups called fibres.
Cellulose ia a mjor component in cell
walls. This provides rigidity and also
prevents cells from bursting due to
osmotic movement of water. It does this
by exerting an inward pressure that
stops any further influx of water. As a
result, living plants cells are turgid and
pushed aginst one another, making
herbaceous parts of the plant semi-rigid.…read more

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Cell differentiation
Single celled organisms perform all essential life functions inside the boundary of
a single cell, but they are not efficient at all of them. Each function requires a
different cell structure. No one cell can provide the best conditions for all
Each cell becomes specialised in structure to suit
the role that it will carry out. This is called cell
differentiation.…read more

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Organ systems
Organs work together as a single unit known as organ system.
These systems may be grouped to perform particular functions more efficiently.
For e.…read more


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