Chapter 4

Question 1

What are some few points about cells?

Answer 1

• 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.

Question 2

What is the immediate environment of a cell which surrounds it with fluid?

Answer 2

Tissue fluid or extracellular fluid

Question 3

Define extracellular and tissue fluid

Answer 3

Extracellular fluid is the fluid found outside the cell; which includes tissue fluid and blood plasma.
( Also known as tissue fluid.)

Question 4

Define Homeostasis

Answer 4

It is the maintenance of a relatively content internal environment despite fluctuations in the external environment.

Question 5

Cell requirements

Answer 5

• 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

Question 6

Explain Cellular respiration (formula + what happens)

Answer 6

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.

Question 7

How do substances get into and out of the cell?

Answer 7

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.

Question 8

What are the functions of the cell membrane

Answer 8

• 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.

Question 9

Explain the fluid mosaic model

Answer 9

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

Question 10

What is the main structure of the cell membrane composed of?

Answer 10

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

Question 11

What is embedded in the phospholipid bilayer?

Answer 11

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.

Question 12

What substances moves across the membrane?

Answer 12

H2O, Glucose, O2, CO2, hormones, enzymes, amino acids, ions; K+, Na+, Ca+, alcohol, drugs ect

Question 13

What factors affect the homeostasis?

Answer 13

Fluid levels in the body - Eg H2O
Constant body temperature is maintained at 37°C
Correct levels of molecules/ ions are maintained

Question 14

List the membrane proteins

Answer 14

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

Question 15

Role of channel proteins

Answer 15

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.

Question 16

What does semipermeable or selectively permeable mean?

Answer 16

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.

Question 17

What are Passive and Active Processes?

Answer 17

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.

Question 18

What are the three basic processes result in transport of materials into in or out of a cell.

Answer 18

• 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

Question 19

Explain what a receptor cell does

Answer 19

Receives information to produce a response. Eg hormone, insulin

Question 20

Explain what a Carrier Protein does

Answer 20

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)

Question 21

What does cell identity markers do?

Answer 21

They identify the cell as ‘self’ to prevent it from attack by the body’s immune system

Question 22

What is diffusion

Answer 22

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.

Question 23

Example of diffusion

Answer 23

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.

Question 24

What is concentration or diffusion gradient?

Answer 24

A difference in concentration of a solution, often between the inside and outside of a cell.

Question 25

What is net diffusion?

Answer 25

The movement of particles of a liquid or a gas is they are distributed evenly over the available space; usually taken to mean the net moving of ions or molecules from higher to lower concentration until evenly distributed

Question 26

How are alcohol, steroids, oxygen and carbon dioxide diffuse into the cell.

Answer 26

Alcohol and steroids and other fat soluble substances can easily enter the cells because they can easily diffuse through the lips portions of a membrane.

Oxygen and carbon dioxide can also diffuse through the phospholipid bilayer.

Oxygen diffuses into the cells because it is continuously needed for cell respiration. The concentration of oxygen inside the cell is therefore lower than the oxygen concentration outside the cell. Because of this concentration difference there is net of oxygen into the cell.

It is similar for carbon dioxide but there is net diffusion for carbon dioxide Out of the cell as it is continually produced in the cell.

Question 27

How does water - soluble molecules pass through membrane?

Answer 27

To diffuse into a cell, water - soluble molecules must pass through protein channels in the membrane which are very small in diameter for larger molecules to enter, but water and ions can easily get through.

Question 28

What is osmosis

Answer 28

It is a special type of diffusion

The discussion of a solvent through a semipermeable membrane.
Osmosis can be considered to be the diffusion of water across semipermeable membrane from one region of high concentration of WATER to a region with lower concentration of WATER

Question 29

What is osmotic pressure?

Answer 29

The pressure dude to differences in the concentration of either side of a semipermeable membrane.

Water moves into or out of a cell by osmosis, depending on the water concentration on each side of the cell membrane - water diffuse from the more ‘watery’ to the less ‘watery’ side I’d a semipermeable membrane

Question 30

What carrier mediated transport

Answer 30

In carrier mediated transport, proteins in the cell membrane bind to molecules to be transported and help their passage across the membrane.

Question 31

What are the important characteristics of carrier-mediated transport?

Answer 31

• the carrier proteins are specific; they sunk only bind to a particular molecule. Eg the carrier which transports glucose cannot transport any other molecule even simple sugars similar to glucose
• carriers can become saturated. - once all available carriers are occupied, any increase in the concentration molecules to be transported cannot incase the rate of movement.
• carrier activity is regulated by substances such as hormones. Hormones are important in coordinating the activities of carrier proteins.

Question 32

What are the two main types of carrier mediated transport?

Answer 32

1. Facilitated diffusion; it is passive. A process which a substance can move with the concentration gradient, from higher concentration on one side of the membrane to a lower concentration on the other.
   - the molecule to be transported (Eg glucose) attaches to a binding site on the carrier. The carrier changes shape and the molecule is released on the other side of the membrane.
2. Active transport. Requires the use of energy. The substances which are transported across the membrane against the concentration gradient, that is to LC-HC. The process of active transport is similar to that of facilitated diffusion, but the big advantage is that it does not depend on a concentration gradient.
   - using active transport a cell is able to take in or pass out substances regardless of their concentration inside or outside of the cell.

Question 33

What is Vesicular Transport?

Answer 33

Vesicular transport is the movement of substances across the cell membrane in membraneous bags called Vesicles.

• it is an active process as energy is needed to form the vesicles.
• there are two types of transport - Endocytosis and Exocytosis

Endocytosis is the taking liquids and solids into the cells by the vesicular transport. The cell membrane will fold around a droplet of liquid or solid particle until it is completely enclosed.
The vesicles so formed then punched off and us suspended into the cell cytoplasm.
* pinocytosis; taking in liquids into the cell via vesicles
* phagocytosis; taking in solids into cell via vesicles

Exocytosis is when the contents if a vesicles inside the cell are passed to the outside. A vesicle that is formed migrates to the cell membrane and fuses with the membrane. The contents of the vesicles are then pushed out into the extracellular fluid

Question 34

Types of transport / passive or active / substance transported

Answer 34

Diffusion / passive / water, ions (ca, k, na, ), O2, Co2, Alcohol, fatty acids, steroids, soluble drugs
* Osmosis/ passive / water (solvent)

Carrier mediated

• facilitated diffusion / passive / glucose, amino acids
• active transport / active / Certain ions, glucose, amino acids

Vesicular Transport

• Endocytosis / Active / cholesterol, iron, micro-organisms, cell debris
• Exocytosis/ Active / secretions Eg mucus, digestive juices

Question 35

Movement within the cell

Answer 35

Endoplasmic reticulum is a network of parallel membranes within the cell.
It is used to transport substances within the cell, particularly proteins that the cell has made.
Transported to the Golgi body for secretion from the cell.

Microtubules are very fine tubes that help maintain the shape of the cell and to hold organelles in place. They also act as train tracks, guiding organelles or molecules to particular places within the cell. Microtubules are not permanent structured but are able to be broken down or built up as needed.