Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

AS BIOLOGY NOTES

F211: CELLS, EXCHANGE AND TRANSPORT
1
...
1 CELL STRUCTURE
a) state the resolution and magnification that can be achieved by a light microscope, a
transmission electron microscope and a scanning electron microscope
...
2 nm

x 500 000

Scanning Electron

0
...

Magnification is the degree to which the size of an image is larger than the object itself
...
Higher resolution means you can see more detail
...

Staining helps to reveal or distinguish different features
...
Some certain chemicals bind to certain organelles or molecules
which would help us to identify the organelles and molecules
...

d) calculate the linear magnification of an image
...


AS BIOLOGY NOTES

f) outline the functions of the structures listed in (e)
...
Extent depends synthesis of lipids
on type of cell

ribosomes

attached to rough
endoplasmic reticulum or
free in cytoplasm

site of protein synthesis

Golgi apparatus

in cytoplasm

synthesis of glycoproteins,
packaging of proteins, makes
lysosomes, lipid synthesis

lysosomes

in cytoplasm

digestion of unwanted
materials and worn-out cells

mitochondria

in cytoplasm
...
You will not be able to see any of the organelles or structures within the cell
...
The
average diameter of a membrane is 7 nm
...

i) Nucleus copies a gene (for the protein) into mRNA
...

iii)Ribosome reads the instructions and assembles the protein
...

Ribosome may be on RER and so vesicle comes from RER
...

vi)Protein may be used in a cell or transported to the plasma membrane in a vesicle where
it binds to plasma membrane and releases protein - exocytosis
...

The cytoskeleton refers to the network of protein fibres found within cells that gives
structure and shape to the cell, and also moves organelles around inside cells
...

Microtubules are small cylinders made of tubulin
...
Other proteins on the
microtubules move organelles and other cell contents along the fibres
...
These proteins are known as microtubule motors and use ATP to drive these
movements
...

Cytoskeleton/microtubules provide tracks for movement
...
This uses ATP
...

They both have a 9+2 arrangement of microtubules, with 9 fused pairs on the outside of a
cylinder and the 2 unfused microtubules in the centre
...

Internal cell movement
The cytoskeleton provides a track on which cells can move organelles, chromosomes and
other things
...


Prokaryotes

Eukaryotes

Average diameter of cell is
0
...
Some organelles are
envelope of two membranes bounded by a single
membrane
Cell wall present

Cell wall sometimes present

j) compare and contrast, with the aid of diagrams and electron micrographs, the structure
and ultrastructure of plant cells and animal cells
...
1
...

Plasma membrane roles;
i) controls movement in and out of the cell
ii)forms a recognition site so body can recognise its own cells
iii)acts as a receptor for hormones
iv)may be folded to form microvilli
v)adhesion of cells
Membranes inside cell roles;
i)provides surfaces on which reactions can occur

AS BIOLOGY NOTES

ii) forms compartments
iii)isolation of contents of organelle/substance
iv)site for attachment of enzymes
v) provide selective permeability
vi)creation of concentration gradients
vii)isolate enzymes
b) state that plasma (cell surface) membranes are partially permeable barriers
...
Cell membranes that are permeable to water and some solutes
are described as partially permeable membranes
...

c) describe, with the aid of diagrams, the fluid mosaic model of membrane structure
...

The main features of the fluid mosaic model are:
i) a bilayer of phospholipid molecules forming the basic structure - the phospholipid tails
point inwards, facing each other and forming a non-polar hydrophobic interior
...
The
phospholipid molecules can move freely within the plane of the membrane
...

iii)some extrinsic proteins partially embedded in the bilayer on the inside or the outside
face; other intrinsic proteins completely spanning the bilayer
...

v)molecules of cholesterol are also found in the membrane
...

Phospholipids - form the bilayer which is the basic structure of the membrane
...
Provide barrier to large or polar
molecules or ions
...
It gives the membranes of some
eukaryotic cells some mechanical stability because the cholesterol fits between the fatty
acid tails and so makes the barrier more complete
...
It also helps to prevent
ions or polar molecules from passing through the membrane
...
They also act as receptor molecules, binding with particular
substances such as hormones or neurotransmitters
...
They also help with cell signalling and act as
receptor sites and help with adhesion
...

Proteins - many proteins in the membrane act as transport proteins
...
Some large and
hydrophilic molecules and ions enter and leave cells using these protein channels
...
This usually happens
against a concentration gradient, using energy from ATP
...
These are for active transport or facilitated diffusion
...
They become denatured when heated
...
They can also act as
antigens
...

- Increasing temperature gives molecules in the membrane more kinetic energy, so they
move faster
...

- The beetroot experiment shows that temperature makes the cell membrane more leaky
so the pigment Betalain leaks out of the cell
...

Cell signaling is the process by which cells communicate with each other to trigger a
response within the cell
...

g) explain the role of membrane-bound receptors as sites where hormones and drugs can
bind
...

They are often protein molecules or modified protein molecules
...

In general;
i) a chemical/hormone is produced and released by a cell
...

iii)chemical/hormone binds to a receptor on the plasma membrane on the target cell
...

v)this will then trigger a response within the target cell
...
The protein has a specific shape
...

Cell surface membranes are involved in cell signaling in the following way;
i) the release of signal molecule by exocytosis
ii)proteins or glycoproteins or glycolipids act as receptors
iii)the receptor is specific
iv)shape of receptor and signal are complimentary

AS BIOLOGY NOTES

v)attachment of signal molecule causes change inside cell
vi)cell surface membrane allows entry of some signal molecules
h) explain what is meant by passive transport (diffusion and facilitated diffusion including
the role of membrane proteins), active transport, endocytosis and exocytosis
...
This occurs due to the natural kinetic energy possessed by the molecules or
ions, which makes them move about at random
...
No extra energy is
needed for this process
...

ii)facilitated diffusion by carrier proteins - these are a specific shape so that only a specific
molecule can fit into them at the membrane surface - when the correctly shaped
molecule fits, the protein changes shape to allow the molecule through to the other side
of the membrane
...

N
...
Fat-soluble molecules can simply pass through the bilayer
...

Very small molecules and ions such as water, carbon dioxide and oxygen can pass
through the membrane by going in between the phospholipid molecules
...


AS BIOLOGY NOTES

Substance moved by:
Simple diffusion

Examples
Small molecules such as
oxygen and lipid-based
molecules like steroid
hormones

Facilitated diffusion - channel Ions like sodium ions and
proteins
calcium ions
Facilitated diffusion - carrier
proteins

Large molecules like glucose
and amino acids

Active transport
Active transport
i) Carrier proteins are used for active transport
...

ii)They carry specific molecules one way across a membrane
...

iv)They carry molecules in the opposite direction to the concentration gradient
...

vi)Molecules can be accumulated either inside cells or organelles, or outside cells
...
This also means that molecules
of the same substance on the other side can not be transported the wrong way as the
shape of the carrier protein has changed and so it is no longer complimentary to the
shape of the molecule
...
The plasma membrane changes shape to surround the material and produces
a vesicle which is taken into the cell
...
Secretory vesicles carry the substance, which has been made in the cell, to the
cell surface membrane
...

Process
Diffusion

Active/Passive
Passive

Facilitated diffusion - channel Passive
proteins
Facilitated diffusion - carrier
proteins

Passive

Active transport

Active

Endocytosis

Active

Exocytosis

Active

AS BIOLOGY NOTES

i) explain what is meant by osmosis, in terms of water potential
...

Water potential is a measure of the ʻfreeʼ water molecules
...
This means that
these water molecules are no longer ʻfreeʼ
...
Whilst a region with no or little solute dissolved in it will
have a high water potential
...

Water molecules will always move from a region of high water potential to a region of
lower water potential
...
Plant cells will
become plasmolysed
...

If a cell is placed in pure water, the water potential inside the cell is lower than outside the
cell, so water moves into the cell by osmosis
...
Plant cell wall
is strong so the cell does not burst
...

1
...
3 CELL DIVISION, CELL DIVERSITY AND CELLULAR ORGANISATION
a) state that mitosis occupies only a small percentage of the cell cycle and that the
remaining percentage includes the copying and checking of genetic information
...

The cell cycle basically consists of interphase and mitosis
...
In interphase the DNA is checked, protein synthesis occurs,
synthesis of organelles occurs, ATP production occurs and cell growth occurs
...

In interphase, the chromosomes have replicated
...
There are four main
stages in mitosis;
i) Prophase - the chromosomes supercoil
...
The
nuclear envelope breaks down and disappears
...

ii)Metaphase - the chromosomes move to the central region of the spindle (the equator)
and each becomes attached to spindle by its centromere
...
The spindle fibres shorten, pulling the chromatids to the poles
...
A new
nuclear envelope forms around each set
...
The
chromosomes uncoil
...
The whole cell splits into two and each cell has a full set of
chromosomes
...


Mitosis differs in plant cells compared with animal cells because;
i) cell plate forms between new cells
ii)cytokinesis starts from middle of cell
iii)only occurs in meristem
iv)no centrioles
c) explain the meaning of the term homologous pair of chromosomes
...
They have the same loci
but the alleles may differ
...
Centromere is in the same position
...

d) explain the significance of mitosis for growth, repair and asexual reproduction in plants
and animals
...
Each new cell is
genetically identical to the parent cells and so can perform the same functions
...

Asexual reproduction - single-celled organisms, such as Paramecium, divide to produce
two daughter cells that are separate organisms
...

e) outline, with the aid of diagrams and photographs, the process of cell division by
budding in yeast
...

Sexual reproduction involves the fusing of two cell nuclei which each contributes half of
the total genetic information (genome) required by the offspring
...
Meiosis is a type of
cell division which produces gametes and it takes place only in specific regions of the adult
organism called the sex organs
...
Importantly;
i) meiosis produces cells containing half the number of chromosomes
ii)meiosis produces cells that are genetically different from each other, and from the parent
cell
...

Stem cells are cells which have the capability to divide and develop into any of several
different cell types
...
They are pluripotent if the cells can develop into several different cell
types
...

Differentiation refers to the changes occurring in cells of a multicellular organism so that
each different type of cell becomes specialised to perform a specific function
...

Xylem and phloem come from dividing meristem cells such as cambium
...

i) describe and explain, with the aid of diagrams and photographs, how cells of
multicellular organisms are specialised for particular functions, with reference to
erythrocytes (red blood cells), neutrophils, epithelial cells, sperm cells, palisade cells,
root hair cells and guard cells
...
They form a thin, smooth, flat surface
...
The parts of the cell which are exposed are
covered with tiny projections called cilia
...

Sperm cells;
i) more mitochondria to generate energy to power the undulipodium
...

iii)they are very small, long and thin
...

v)they contain half the number of chromosomes in their nucleus
...

ii)they are packed with chlorophyll
...

Root hair cells;
i) the cells have a hair-like projection from their surface into the soil
...

ii)when water moves into the cell, the spirals in the cell wall cause the outer cell wall to
stretch, causing it to go banana shaped
...

Tissue - A collection of cells that are similar to each other and perform a common function
...

Organ systems - A number of organs working together to perform an overall live function
...

Squamous epithelial tissues - it is made up of flattened cells so they are very thin
...
This means fluids can easily pass over
them
...
The squamous epithelial cells are held in place by the basement membrane
...
The parts of the cells
which are exposed are covered in tiny projections called cilia
...

This allows bacteria to be trapped in mucus and then wafted to the back of the throat to be
swallowed
...


AS BIOLOGY NOTES

Xylem - it consists of xylem vessels with parenchyma cells and fibres
...
Their walls become reinforced and waterproofed by
deposits of lignin
...
The ends of the cells break down so
that a single continuous tube is produced with a wide lumen
...
Xylem also help to support the cell
...
They are also hollow and have no organelles
...
The meristem tissue produces
cells that elongate and line up end-to-end to form a long tube
...
The sieve plates allow the
movement of materials up or down the tubes
...
Companion cells play an important role in moving products from photosynthesis up
and down the sieve tubes
...
They
also have little cytoplasm and no nucleus
...

l) discuss the importance of cooperation between cells, tissues, organs and organ
systems
...

For example, the cells in the brain must signal the tissues in muscle to contract
...
The oxygen and carbon dioxide which are exchanged in the lungs
both travel in the blood which is part of the circulatory system

---