What are some few points about cells?
- The structure of an organism and how it functions results from the activities of all its cells.
- Human body is comprised of trillions of cells
- Everything we do results from the combined and coordinated actions of the cells
- each cell is and individual unit with requirements that must be satisfied if it is to function normally.
What is the immediate environment of a cell which surrounds it with fluid?
Tissue fluid or extracellular fluid
Define extracellular and tissue fluid
Extracellular fluid is the fluid found outside the cell; which includes tissue fluid and blood plasma.
( Also known as tissue fluid.)
Define Homeostasis
It is the maintenance of a relatively content internal environment despite fluctuations in the external environment.
Cell requirements
- For a normal functioning, cells in the body need to be in a stable environment
- They must have continual supply of the materials they need
- They must have continual removal Of any material they produce
- To carry out their function the cells need a certain substance/s that must be taken in from the tissue fluid.
- As substances are processed in the cell, materials produced must be removed from the cell
- Different cells have different requirements and products, depending on the particular role of the cell
Explain Cellular respiration (formula + what happens)
Food + Oxygen -> Energy + Carbon Dioxide + Water
C6H12O6 + O2 -> Energy + CO2 + H2O
One requirement all cells need is oxygen for respiration.
The process of respiration releases the energy needed for the cell’s activites.
Glucose is also need for respiration, the substance that is broken down to release energy.
Respiration produces carbon dioxide and water, substances that cannot be allowed to accumulate in the cell. Thus they are released to tissue fluid.
How do substances get into and out of the cell?
Each cell is surrounded by a cell membrane (also called a Plasma membrane).
It is a very thin layer of plasma ( cannot be seen with a light microscope)
Substances that leave or enter the cell must pass through the cell membrane, so the cell membrane is very important in detecting what goes goes into and out of the cell.
What are the functions of the cell membrane
- acts as a physical barrier - the membrane separates the cell cytoplasm from the extracellular fluid around the cell. The isolation of the cytoplasm from the surrounding fluid tissue is important as the composition of the cytoplasm and the extracellular fluid is very different.
- Regulates the passage of materials- the membrane controls the movement of the of materials in and out of the cell.
- Supports - the internal part of the cell membrane is attached to the microfilaments of the cell’s cytoskeleton, thus giving support to the whole cell. Also the connections between the membranes of the adjacent cells gives support to the whole tissue which the cells are a part.
- Sensitivity- the cell member is the first part of the cell affected by any changes in the extracellular fluid. It also has receptors that are sensitive to particular molecules in its immediate environment.
Explain the fluid mosaic model
It is the currently accepted model of a cell embrace structure
Fluid because the molecules of which it is made are Constable changing position
Mosaic because of the composition and pattern of the different kinds of molecules
What is the main structure of the cell membrane composed of?
The main building blocks of a membrane are Phospholipid molecules
- which are lipid molecules (fatty) contains a phosphate group.
- The phospholipids are arranged into two layers called a ‘Bilayer’
- Each phospholipid has a head that is hydrophilic ( water loving and is polar) and a tail that hydrophobic (water hating)
- head will be on the outside (cytoplasm and extracellular fluid) whereas as the tails will be in the middle.
- they will drift from place to place with the head and tails moving, keeping the membrane fluid.
- they also have a glycerol backbone
What is embedded in the phospholipid bilayer?
In the phospholipid bilayer there is cholesterol and protein molecules embedded in it.
The cholesterol molecules and wedged between the phospholipid.
Some protein molecules pass through the membrane from one side to the other while others are bound to the surface of the membrane.
What substances moves across the membrane?
H2O, Glucose, O2, CO2, hormones, enzymes, amino acids, ions; K+, Na+, Ca+, alcohol, drugs ect
What factors affect the homeostasis?
Fluid levels in the body - Eg H2O
Constant body temperature is maintained at 37°C
Correct levels of molecules/ ions are maintained
List the membrane proteins
Only 2% of the cell but make up 55% of weight as they are very large molecules
- Channel Proteins
- Carrier Proteins
- Receptor Proteins
- Cell - Identity markers
Role of channel proteins
They form a channel through the membrane and have a central pore that which is large enough to only allows ions, water and small molecules to pass through.
What does semipermeable or selectively permeable mean?
The cell membrane will only allow certain ions and molecules to pass through, but restricts the movement of other which are larger.
Also known as differentially permeable.
What are Passive and Active Processes?
Materials that are too large to pass through the semipermeable cell membrane may pass though it in other ways.
Some transfer mechanisms are PASSIVE Processes; this means the cell’s energy which comes from respiration does not have to be used.
Other transfer mechanisms are ACTIVE processes; that do require the cell’s energy for the transfer to occur.
What are the three basic processes result in transport of materials into in or out of a cell.
- Diffusion; a passives process - resulting from the random movement of ions and molecules
- Osmosis (also passive) is a way in which diffusion can occur where water passes across a membrane from high concentration to to low concentration.
- Carrier mediates transport - it is a process that requires special proteins in the cell membrane; it may be Passive or Active depending on the exact nature of the mechanism.
- Vesicular Transport- (Active) a process in which materials are moved in membrane-bound sacs
Explain what a receptor cell does
Receives information to produce a response. Eg hormone, insulin
Explain what a Carrier Protein does
They are specific, only allows certain molecules to bind to it.
Eg glucose, amino acids
Allows facilitated diffusion (Eg. Glucose) and active transport ( specific membrane pumps)
What does cell identity markers do?
They identify the cell as ‘self’ to prevent it from attack by the body’s immune system
What is diffusion
Diffusion is the spreading out of particles so that they are evenly distributed over the space available.
It colours in liquids and gases because the molecules of liquids and gases are constantly moving; moving in random directions and un straight lines until they hit another molecule or obstacle.
The molecule will move from a high concentration area to a lower concentration area of that molecule, to prevent collisions and freely move.
Random movement of molecules moving continues, But the chances if collision are the same in whatever direction the molecule is travelling.
Example of diffusion
Perfume in the air
Sugar (solute) in water (solvent) will dissolve and become a solution. The sugar molecules will be evenly spread throughout the water.
What is concentration or diffusion gradient?
A difference in concentration of a solution, often between the inside and outside of a cell.
