Cells and Tissues

Question 1

Cell Structure

Answer 1

Cells are made up of Organelles which are structures suspended in the cytoplasm that carry out a particular function.

Question 2

Cell Membrane

Answer 2

Location: Surrounding the cell (separates extracellular fluid from intracellular fluid)
Description: Made of phospholipid bilayer
Function: Controls which substances enter and leave the cell

Question 3

Cytoplasm

Answer 3

Location: Inside the cell
Description: Thick-watery fluid that suspends cell organelles
Function: Contains dissolved ions, salts & carbohydrates. Where some chemical reactions take place.

Question 4

Nucleus

Answer 4

Location: Inside the cell
Description: Contains the genetic material/ DNA
Function: Contains the DNA which codes for protein production in the cell
Nucleolus: Suspended in nucleoplasm Contains RNA
Nuclear Membrane: Separates nucleus from cytoplasm. Contains pores for movement of molecules

Question 5

Mitochondria

Answer 5

Location: Inside the cell
Description: Contains folded membranes to increase surface area
Function: Where cellular respiration occurs to release energy for the cell

Question 6

Endoplasmic Reticulum

Answer 6

Location: Inside the cell
Description: Series of flattened, sac-like membranes that extend throughout the cytoplasm
Rough ER: lined with ribosomes
Smooth ER: no ribosomes
Function: Transports proteins around the cell and involved in the manufacture of lipids

Question 7

Ribosomes

Answer 7

Location: Lining the rough endoplasmic reticulum or free in the cytoplasm
Description: Small organelles
Function: Where proteins are constructed from amino acids

Question 8

Golgi Body

Answer 8

Location: Positioned near nucleus and surrounded by vesicles
Description: Consists of parallel smooth membranes
Function: Packages proteins, lipids and carbohydrates into vesicles for export from the cell

Question 9

Vesicles

Answer 9

Location: Inside the cell
Description: Membrane bound organelle
Function: Stores materials for secretion from the cell

Question 10

Lysosomes

Answer 10

Location: Inside the cell
Description: Membrane bound vesicles
Function: Contains digestive enzymes to break down foreign material in the cell

Question 11

Centrioles

Answer 11

Location: Inside the cell
Description: Tube-like structures at 90 degrees to one another
Function: Produce spindle fibres which assist in separation of chromosomes during cell division.

Question 12

Microtubules

Answer 12

Location: Inside the cell
Description: Rod-like structures
Function: Keep organelles in place or move them around the cell

Question 13

Cell Functions features and function

Answer 13

Cell Requirements:
The body systems work together to make sure the cellular environment is kept constant; this is called Homeostasis.
Exchange of nutrients and wastes is continually occurring between the extracellular fluid (fluid between the cells) and the cell to maintain balance.
The cells are also maintained at a constant temperature and concentrations of fluids.

Functions of Cell Membrane:
Physical Barrier:
Separates the contents of the cell (INTRACELLULAR) with the outside of the cell (EXTRACELLULAR) that have different compositions
Note: Extracellular fluid includes Tissue fluid (Intercellular / Interstitial fluid) & Blood plasma

Regulates what enters and leaves cell:
“Differentially/ Selectively Permeable”
Maintains Homeostasis

Sensitivity:
First part of the cell affected by any changes in the extracellular fluid.
Receptors that are sensitive to particular molecules
Support:
Attached to cytoskeleton

Question 14

Fluid Mosaic Model

Answer 14

Fluid – molecules constantly changing position
Mosaic – made of lot of different molecules

Question 15

Cell Membrane Structure

Answer 15

• Main structure is made of Phospholipid molecules (lipids attached to a phosphate group)
• Arranged in a “Bi-Layer”
• Hydrophilic head and Hydrophobic tail
• ‘Hydro’ – Water,
• ‘philic’ – ‘loving’
• ‘phobic’ – ‘hating’
• Embedded in phospholipid bi-layer are cholesterol molecules. These stiffen the membrane while also maintaining fluidity.
• The membrane is also embedded with a variety of proteins:
• Channel Proteins
• Carrier Proteins
• Receptor Proteins
• Cell-identity markers / Recognition Proteins

Question 16

Cell Membrane Proteins

Answer 16

CHANNEL PROTEINS:
• Form a channel through the membrane for smaller molecules to pass through
• Used for simple diffusion

CARRIER PROTEINS:
• Bind to larger molecules and help them move across the membrane
• Used for Facilitated diffusion or Active transport

RECEPTOR PROTEINS:
• Molecules outside the cell can bind with receptor proteins to cause a change within the cell.
• Each type of receptor will only bind with one particular molecule
• SPECIFIC – “LOCK AND KEY MODEL”
• Some hormones work in this way:
• The hormone Insulin binds to a specific receptor protein and this leads to an increase in glucose absorption by the cell.

RECOGNITION PROTEINS:
• Have a carbohydrate group projecting out of the cell which act as ID tags, allowing the cell to be recognised as “self” or a foreign cell, “non-self”.
• Identifies the cell to prevent attack by the body’s immune system

Question 17

Cell Transport Requirements

Answer 17

Inputs: Oxygen, Water, Nutrients (glucose, amino acids, lipids), Hormones, Vitamins & minerals, Ions (Na +, Cl-, K+ etc)
Outputs: Carbon dioxide, Wastes (toxins, urea), Water, Hormones / secretions

Question 18

Transport through Cell Membrane

Answer 18

To enter or exit the cell, substances need to cross the membrane. Either through the:
• phospholipid bilayer, or Channel/carrier proteins.
• The cell membrane is selectively permeable – i.e. It allows some substances to cross more easily than others.

Transport processes are either passive or active. Passive processes require NO cellular energy. These include:
• diffusion, osmosis & facilitated diffusion.
• Active processes require energy (ATP molecule) and include membrane pumps to move substances.

How each substance moves is determined by its:
• Composition
• Concentration
• Size

Question 19

Diffusion

Answer 19

• Diffusion is the spreading out of particles so that they are evenly distributed over the space available.
• Gases or liquids will travel from an area of high concentration to areas of lower concentration.
• This is known as a concentration gradient.

Diffusion through the membrane:
• The cell membrane is a lipid bilayer (fat), most water-soluble substances cannot diffuse through it.
• Substances that will diffuse through the cell membrane include oxygen and carbon dioxide and fat-soluble substances such as alcohol and steroids.

The rate (how fast) the particles diffuse depends on the following factors:
• Concentration gradient
• Surface area
• Permeability of the membrane
• Size of the particles
• Temperature

Question 20

Concentration Gradient

Answer 20

When the concentration of a substance is different at two places, the substance will diffuse ‘down’ the concentration gradient until the concentration in the two areas becomes equal.

Question 21

Osmosis

Answer 21

• This is the diffusion of water across a selectively permeable membrane.
• Water is not fat-soluble therefore cannot diffuse through the membrane, instead it travels through channels in the membrane.
• Water molecules move from high to low concentration.
• This is a passive process. (Does NOT need ATP – energy.)

Question 22

Why does Water move (Osmosis)

Answer 22

• Water moves if there are solutes (i.e. glucose or sodium etc.) in one area that cannot escape.
• This can occur because the water molecules are small enough to fit through the channels in the membrane but the glucose or other molecules are trapped, as they are too large to fit through the channel.
• Remember, science is all about balance (equilibrium), the water is moving to dilute the concentration of other molecules on the other side of the membrane.
• More water on one side of a membrane to the other creates pressure, this is known as osmotic pressure.
• Hypertonic: a solution that has more/higher concentration of solutes. (High osmotic pressure) Eg, a cell sitting in a salty solution
• Isotonic: having the same concentration solution in and out of the cell.
• Hypotonic: a solution that has less/lower concentration of solutes. (Low osmotic pressure) Eg, a cell sitting in a distilled water solution

Question 23

Facilitated Diffusion

Answer 23

• Facilitated diffusion is a process of diffusion where molecules diffuse across the cell membrane with the assistance of transport proteins
• The molecules bind to the protein which changes the configuration/shape of the protein, to deposit the molecule across the membrane
• Examples: Glucose and amino acids
• ATP? No as it’s diffusion (passive)
• Concentration Gradient? Areas of high to low
• Lipid Soluble? No, it’s going through a carrier which is water soluble, otherwise it would’ve gone through a membrane.
• Size? Small yet a little bit of a bigger molecule since it needs assistance

Question 24

Active Transport

Answer 24

• Requires energy (ATP)
• Substances more from low to high concentration (against concentration gradient)
• This uses membrane pumps (carrier proteins) to do this

Question 25

Endocytosis

Answer 25

• Endocytosis is the process where substances enter a cell inside a vesicle (bubble).
• It involves cells absorbing large particles such as proteins (or even whole organisms such as bacteria & viruses) from the extracellular fluid.
• It does this by engulfing them with their cell membrane to form a vesicle within the cytoplasm.
• This requires energy.
• There are 2 special types of endocytosis:
• When a liquid is engulfed, it is called pinocytosis. (Cell drinking)
• When a solid is engulfed, it is called phagocytosis. (Cell eating)

Question 26

Exocytosis

Answer 26

• When substances are packaged and leave the cell in a vesicle it is called exocytosis.
• The golgi apparatus is responsible for this process.
• Requires energy.

Question 27

Organisation of the Body (Tissues)

Answer 27

• Cells are the basic building block.
• Cells make up tissues, tissues make up organs and organs make up systems.
• Cells > Tissues > Organs > Systems
• Tissues – are made of groups of cells that are similar in structure and work together to carry out a task.
• Organs – made of two or more different types of tissues that work together.
• System – a group of organs that work together for a common purpose.

Question 28

Epithelial Tissue

Answer 28

• Covering or lining tissue
• All body surfaces, cavities, glands and ducts
• Cells are very close together with little intercellular fluid between them
• Vary in shape from thin and flat, to columned and cubed

Question 29

Connective Tissue

Answer 29

• Holds parts of the body together and provides support
• Cells are not as close together (as epithelium), they are separated by large amounts of material called matrix.
• Examples include loose and dense connective tissues, cartilage, adipose tissue (fat), bone and blood.

Question 30

Muscular Tissue

Answer 30

• Contains muscle fibres which contact becoming shorter to contract the muscle.
• They are elastic, meaning they can return to their original shape.
• They are also excitable, meaning they respond to nerve impulses.

There are 3 types:

Skeletal muscle:
• Muscles that are attached to our skeleton.
• Striped appearance referred to as STRIATED.
• Controlled voluntarily.

Smooth / Involuntary muscle:
• Muscles that make up our organs.
• No striations so referred to as SMOOTH or NON-STRIATED.
• Cannot be controlled involuntarily.

Cardiac muscle:
• Muscle of the heart.
• Faint striations.
• Cannot be controlled voluntarily.

Question 31

Nervous Tissue

Answer 31

• Made up of specialised cells called neurons, which have long projections form the nerve cell body.
• Receive and transmit messages as electrical impulses.
• Brain, spinal cord and nerves.