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#14 Cell structure

Most living things are made of cells
...

Plant and animal cells differ in size,
shape and structure (plants cells are
usually larger than animal cells)
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Each type of
cell is design for a particular function
...
Ciliated cells in respiratory tract
Features: tiny hairs called cilia which can move mucus
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2
...

Function: cause movement

3
...
Root hair cell (plants)

Features: the hair gives
a large surface area
Function: absorb water
and mineral ions; anchor
the plant firmly in soil

5
...
The
cells lack end wall and cell contents such as cytolplasm and nucleus
...

Function: conduction (transport water and mineral ions from roots to
leaves)
support (Ligmin provides strength for the stem)
...
Xylem carries water and
mineral salts, while Phloem transports sugars and amino acids
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Examiner's tips
1
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A leaf is an organ made up of a
number of tissues, e
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upper epidermis, palisade, mesophyll
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If you draw a diagram to support an exam answer, make sure you
refer to its in your written answer
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Example of annotation
Action of phagocyte

#16 Tissues, Organs and organ Systems

Cells are organized to form tissue, organs, and organ
systems
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SPECIALIZED CELLS






A specialized cell is designed to do a particular job
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Muscle cells can contract and relax
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Platelets help clotting
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Muscles, blood and nerves are all tissues
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Each organ has its own specific job
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The heart has to pump blood around the body
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Arteries and veins are usually thought of as organ as they consist of
several tissue layers
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E
...
the circulatory
system carries blood to all parts of the body
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ORGANISM
Various organ systems together make up an organism
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g
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Tissue: a group of cells with similar structures, working together to
perform a shared function
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Organ system: a group of organs with related functions, working
together to perform body functions
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Molecules
move down a concentration gradient, as a result of their random
movement
...

The simplest sort of selection is based on the size of the molecules
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There is
a lower concentration of CO2 inside the leaf, as the cells are using it
up
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Flowering plants use diffusion to attract pollinators like bees
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Site of diffusion
Alveoli of lungs
Stomata of leaf

Substance
O2
CO2
O2

Description
Alveoli à Blood capillaries
Blood capillaries à Alveoli
Air spaces of leaf à Atmosphere

Factors favoring diffusion







Distance (the shorter the better), e
...
thin walls of alveoli and
capillaries
...
This can be
maintained by removing the substance as it passes across the diffusion
surface
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Size of the molecules (the smaller the better)
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Temperature (molecules have more kinetic energy at higher
temperature)
...

Many substances move around a cell dissolved in water
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Additional resource: http://askmichellebiology
...
com

#18 Osmosis
Osmosis is the diffusion of water molecules from a
region of their higher concentration to a region of
their lower concentration, through
a partially permeable membrane
...
Osmosis is:




the movement of H2O
across a selectively permeable membrane
down a water potential gradient
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- The concentration of water molecules is higher on the (R) and lower on
the (L) (a lot of place is taken up by sugar molecules)
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There is a water potential gradient between the 2 sides
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Cell membranes




partially permeable (let some substances pass through, but not
others)
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If the solutions are of different concentrations, osmosis will occur
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When placed in H2O:
Concentration of H2O outside the cell
is higher than inside it
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animal cells will burst (no cell
wall)
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When placed in concentrated sugar
or salt solutions:
Concentration of H2O inside the cell
is higher than outside it
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The plant loses it firmness and begin
to wilt
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Common misconceptions
Sugar and salt do not move by osmosis
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Try this
A potato was set up as shown in the figure below (left-hand side)
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The results are shown on the righthand side of the figure
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Describe what happened to
a
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the salt solution in the hollow in the potato
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[2 marks]

a
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[1 mark]
b
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[3 mark]
c
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What is the importance to the plant of this process? [1 mark]
Answers
1
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The volume of water in the dish decreased
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The volume of salt solution in the potato increased
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a
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3 points from:
- there was a higher concentration of water in the dish than in the potato
- so water moved into the potato
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c
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d
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#19 Active transport
Sometimes substances are required to
be move against the Concentration
Gradient, or faster than they would by
Passive Transport
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There are many occasions when cells need to take in substances which are
only present in small quantities around them
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g
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Their
concentration are often higher inside the root hair cell than in the soil, so
the diffusion gradient is from the root hair à the soil
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The importance of active transport: energy-consuming process by which
substances are transported against a concentration gradient, e
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ion uptake
by root hairs and glucose uptake by epithelial cells of villi
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Try this

Figure above shows root hair cells
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Explain how the presence of root hair cells on roots enables the
efficient absorption of water and minerals
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Root hair cells can absorb mineral ions by diffusion and active
transport
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- Large number of root hair cells give a large surface area to the root
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2
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- using energy
b) active transport requires energy

#20 Sum mary of Cells

Structure


Cells are the smallest units of living things
...




Cells have a cell membrane, cytoplasm and a nucleus
...




The cell membrane is partially permeable, and it controls what
enters and leaves the cell
...
It is the site of many different metabolic reactions
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This is the genetic information and it controls the activities of the cell
...
It is fully permeable
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

The vacuole of a plant cell contains cell sap, which is a solution
of sugars and other substances in water
...
There may be starch grains inside the

chloroplasts, which are the form in which plants store the food that
they make in photosynthesis
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Tissues are grouped into organs, and organs are
grouped into organ systems
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As a result of this, there is a net movement from where they are in
a high concentration to where they are in a low concentration
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

Diffusion is important to cells
...




Water molecules are small and can diffuse through a partially
permeable membrane
...
The diffusion of water through a partially permeable
membrane is called osmosis
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In a dilute solution, water passes into
a cell through its partially permeable cell membrane
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Animal cells may burst, but plant cells do not because of
their strong cell wall
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The cell shrinks
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

A solution containing a lot of water is said to have a high water
potential
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Water moves by osmosis down a water potential
gradient, from a high water potential to a low water potential
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This is
called active transport
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