Topic 2 notes

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  • Created on: 25-04-16 16:41
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Surface area to volume ratio : the amount of surface area per unit volume of
an object or collection of objects.
The higher the SA: V ratio , the more effective the process of diffusion.
The respiratory system provides a large surface area to volume ratio to
ensure efficient gas exchange .
Adaptation of lungs for exchange:
1. Large surface area for molecules to diffuse through. This increases
rate of diffusion (alveoli)
2. Permeable barrier for oxygen and carbon dioxide to be easily diffused
3. Thin barrier (flattened epithelial cells) which reduces diffusion
distance (alveoli, capillary wall is one cell thick)
4. Maintain steep concentration gradient having fresh supply of
molecules to keep concentration high and removal of required
molecules to keep concentration low
Beetroot experiment: the higher the temperature, the more colour leaked
out from the beetroot and hence the more damage is done to the cell
membrane . The fatty acid tails of the phospholipid bilayer begin to denature
at high temps and cholesterol loses its structure, meaning the bilayer
becomes more fluid allowing more movement. This affects permeability of
cell which allows foreign molecules to enter.

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The fluid mosaic model describes the plasma membrane of animal cells. It is
mosaic is structure because it is embedded with proteins of all different sizes.
It is considered fluid because it doesn't have an entirely rigid structure.
Component Structure/Description Function
Phospholipid hydrophilic phosphate forms bilayer
heads impermeable barrier
hydrophobic fatty acid
Cholesterol type of lipid stability and strength
small holds phospholipids
Glycoprotein insoluble protein with cell signalling and cell
carbohydrate chain recognition.
attached.…read more

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Osmosis: the movement of water molecules from an area where they are in
high concentration to an area of lower concentration through a partially
permeable membrane .
Water molecules form hydrogen bonds with solutes, reducing the movement
of water molecules.
Through phospholipid bilayer.
Passive, no energy required.
Passive transport: a kind of transport by which ions or molecules move along
a concentration gradient (i.e. from high to low conc.). No energy is required.…read more

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ATP supplies energy to change the shape of a carrier protein molecule when
substances are moved against the conc. gradient.
Endocytosis bulk transport of substances into a
cell by the creation of a vesicle.
Exocytosis bulk transport of substances out of
the cell.
vesicles fuse with the cell surface
membrane and the contents are
A mononucleotide is made up of a 5carbon sugar
(either ribose or deoxyribose), a phosphate group and
a base (adenine, cytosine, guanine, thymine or uracil).…read more

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RNA the pentose sugar is called ribose and the base uracil replaces the base
There are 3 different types of RNA:
mRNA (messenger RNA) ­ it acts as a copy of a gene by having a
sequence complementary to one strand of DNA and identical to the
other strand. It carries the info stored in the DNA in the nucleus to the
cytoplasm where the ribosomes can make it into a protein .…read more

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The genetic code in the DNA making up the chromosomes acts as a code for
protein synthesis .
It dictates the order of the amino acids required to make the protein and the
order in which they should be bonded together.
3 bases code for 1 amino acid and these base triplets are nonoverlapping .
Since RNA is constructed from four types of nucleotides , there are 64 possible
triplet sequences or codons (4x4x4).…read more

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Fibrous and Globular
Fibrous Globular
Repetitive regular sequences of Irregular amino acid sequences.
amino acids
Actual sequences may vary slightly Sequence highly specific and never
between 2 examples of same varies between 2 examples of same
protein. protein.
Polypeptide chains form long parallel Polypeptide chains folded into a
strands. spherical shape.
Length of chain may vary in 2 Length always identical in 3 examples
examples of same protein. of same protein.
Stable structure. Relatively unstable structure.
Insoluble Soluble
Support and structural functions. Metabolic functions.
e.g.…read more

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Extracellular reactions: reactions occurring outside a cell.
Increase in temperature (increase in kinetic energy to molecules), increases
likelihood of collisions between enzyme and substrate molecule. Hence rate
of reaction increases. Beyond the optimum temperature , the increased
vibration of the atoms in the protein molecule break the bonds maintaining
the tertiary structure. The active site is denatured .
pH changes around the enzyme's optimum pH , altering the charge
distribution in the active sie, reducing the compatibility of enzyme and
substrate.…read more

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Two new double
helices result, each containing one new strand and one old strand.
Sometimes, the DNA does not replicate properly ­ an incorrect base may slip
into place = a gene mutation .
If it occurs in the sperm or ovum , which form a zygote, every cell in the new
organism will carry the mutation . If it occurs in noncoding DNA , it will have
no effect .…read more

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In humans, recessive mutations of single genes result in:
o Cystic Fibrosis : mucus which is too viscous.
o Thalassaemia : abnormal haemoglobin formation.
o Albinism : lack of pigment production.
Gregor Mendel initiated the study of genetics using the garden pea. He
established patterns of inheritance of a number of phenotypes incl. height
and the morphology of seeds .
In the respiratory system , the amount of water in the mucus must be
regulated because:
i. Too runny mucus floods the airway .…read more





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