Biology Mock - Paper 1 Flashcards
Units Of Measurement?
1 Kilometre = 1000 metres
1 Metre = 1000 man
1 Millimetre = 1000um
1 Micrometre = 1000nm
Osmosis Is?
Movement of water from a high water potential to a low water potential through a permeable membrane.
Phospholipids Properties?
Similar to lipids except that one of the fatty acid molecules is replaced by a phosphate molecule,
Fatty acids repel water (are hydrophobic), phosphates attract water (are hydrophilic),
A phospholipid is made of two parts:
- hydrophilic ‘head’ which interacts with water but not with fat,
- hydrophobic ‘tail’ which orients itself away from water but mixes readily with fat,
Molecules that have two ends (poles) that behave differently in this way age said to be polar,
This means when these polar phospholipid molecules are placed in water, they position themselves so that the hydrophobic are as far away from water and possible and the hydrophilic are as close to water as possible.
The phospholipids are part of the bilateral of a plasma membrane.
Cell Specialisation Is?
The cells of multicellular organisms are specialised in different ways to perform a particular role.
The first group of cells in an embryo are identical. As it matures, each cell becomes specialised to suit the role that will carry out.
Cells become specialised when different genes are switched on to allow a cell to make certain functions and the rest are switched off.
What’s A Plasma Membrane?
All membranes around and within cells have the same basic structure and are known as plasma membranes.
Also known as ‘cell-surface membrane’.
It surrounds cells and forms the boundary between the cell cytoplasm and the environment.
It allows different conditions to be established inside and outside a self.
It controls the movement of substances in and out of the cell.
They are permeable to small, non-polar molecules, like oxygen.
The fluid-mosaic model models the cell-surface/plasma membrane.
What Structures Form The Plasma Membrane?
- Phospholipids (to form the phospholipid bilayer),
- Proteins (protein channels and carrier proteins),
- Glycolipids,
- Glycoproteins,
- Cholesterol.
Phospholipid Functions?
Polar molecules (hydrophobic and hydrophilic properties) so in an aqueous environment, phospholipids form a bilayer within cell-surface membranes and hydrophobic barriers are created inside and outside the cell,
Hydrophilic phosphate heads help to hold the surface of the cell-surface membrane together,
Phospholipid structure allowed them to form glycolipids by combining with carbohydrates within the cell-surface membrane. These glycolipids are important in cell recognition.
They allow for lipid-soluble substances to enter and leave the cell.
They prevent water-soluble substances entering and leaving the cell.
They also make the membrane flexible and self-sealing.
What Is A Tissue?
A collection of similar cells that perform a specific function is a tissue.
Examples include:
- epithelial tissues,
- xylem.
Some tissues are then arranged into organs.
Carrier Proteins?
An alternative form of facilitated diffusion involves carrier proteins.
Found in plasma membrane (phospholipid bilayer).
When a molecule (such as glucose) that is specific to the protein is present, it binds with the protein.
This causes it to change shape in such a way that the molecule is released to the inside of the membrane.
No external energy is needed for this.
The molecules move from a high concentrated to a low concentration, using only the kinetic energy of the molecules themselves.
Protein channels and carrier proteins have binding sites, not active sites.
Protein Channels?
Part of the cell-surface (plasma) membrane.
These proteins form water-filled hydrophilic channels across the membrane.
They allow specific water soluble ions to pass through.
The channels are selective, each opening in the presence of a specific ion.
If the particular ion is not present, the channel remains closed.
The ions bind with the protein causing it to change shape in a way that closes it to one side of the membrane and opens it to the other side.
Protein channels and carrier proteins have binding sites, not active sites.
What Is The Purpose For Proteins In A Plasma Membrane?
- Providing structural support,
- Act as channels for water-soluble substances for transport across membrane,
- Allow active transport across the membrane through carrier proteins,
- Form cell-surface receptors for identifying cells,
- Help cells adhere together,
- Act as receptors, for e.g. hormones.
Cholesterol In A Plasma Membrane?
Cholesterol molecules occur within the phospholipid bilayer of the cell surface membrane.
They add strength to the membrane.
They are very hydrophobic and so prevent loss of water and loss of dissolved ions from the cells.
They pull together the fatty acid tails of the phospholipid molecules, limiting their movement and that of other molecules but without making the membrane too rigid.
In summary:
They reduce lateral movement of other molecules including phospholipids.
They make the membrane less fluid at high temperatures.
They prevent leakage of water and dissolved ions from the cell.
Glycolipids In Plasma Membrane?
Glycolipids are made up of a carbohydrate covalently bonded with a lipid.
The carbohydrate portion extends from the phospholipid bilayer into the watery environment outside the cell. Here, the carbohydrate acts as a cell surface receptors for specific chemicals (for example the human ABO blood system operates as a result of the glycolipids on the cell surface membrane).
Functions:
- Acts as a recognition site.
- It helps maintain the stability of the membrane.
- Glycolipids also help cells to attach to one another and so form tissues.
Glycoproteins In Plasma Membranes?
These glycoproteins also act as cell-surface receptors, more specifically for hormones and neurotransmitters.
Functions of glycoproteins in membrane:
- Act as recognition sites,
- Help cells to attach to one another and so form tissues,
- Allows cells to recognise one another, for example lymphocytes can recognise an organisms own cells.
What Molecules Diffuse Into The Plasma Membrane And What Molecules Don’t?
Molecules must be one of the following to diffuse across the plasma membrane.
Must be:
- Soluble in lipids so they can pass through phospholipid bilayer.
- Small enough to pass through channels.
- Of a different charge as the charge on protein channels and so, even if they are small enough to pass through, they are not repelled.
- Not electrically charged (non-polar) because if they are electrically charger (polar), they will have difficulty passing through non-polar hydrophobic tails in the phospholipid bilayer.
