Specialised Cells and Stem Cells

Question 1

Outline the levels of organisation of a multicellular organism (in order).

Answer 1

Organelle, Cell, Tissue, Organ, Organ system, Organism

Question 2

Define specialised

Answer 2

Having a particular structure to serve a specific function.

Question 3

Define differentiation

Answer 3

The process of a cell becoming differentiated. Involves the selective expression of genes in a cell’s genome.

Question 4

Define the term cell

Answer 4

A basic unit of life. Consists of cellular contents surrounded by a plasma membrane . All life is composed of these basic units whether it is unicellular or multicellular

Question 5

Define the term tissue

Answer 5

A collection of differentiated cells that work together to perform a specialised function or functions.

Question 6

Define the term organ

Answer 6

A collection of tissues that work together to perform a particular function in an organism

Question 7

Define the term organ system

Answer 7

A number of organs working together to carry out a major function in the body.

Question 8

Describe how neutrophils are specialised for their funciton

Answer 8

Functions- Defend the body from disease
Structure:
1. They have a flexible shape- allows them to engulf foreign particles or pathogens.
2. Multi-lobed nucleus- easier to squeeze through small gaps to get to site of infections.
3. Cytoplasm contain many lysosomes- they contain digestive enzymes to break down the engulfed particles

Question 9

Describe how sperm cells are specialised for their funciton

Answer 9

Function- deliver genetic information to the female gamete
Structure:
1. Have a flagellum- capable of movement
2. They have lots mitochondria- to provide energy to swim
3. Acrosome on the head contains digestive enzymes- released to digest the protective layers around the ovum, allowing the sperm to penetrate.

Question 10

Describe how palisade cells are specialised for their function

Answer 10

Function- to do most of the Photosynthesis
Structure:
1. Contain many chloroplasts- absorb large amounts of energy for photosynthesis
2. The cells are a rectangular box shape- can be closely packed to form a continuous layer.
3. Have thin cell walls- increase the rate of diffusion of CO2

Question 11

Describe how root hair cells are specialised for their funciton

Answer 11

Function- Absorb mineral ions and water from the soil
Structure:
1. Have lots of root hairs (long extensions)- increase SA of cell, to maximise uptake of water and minerals
2. Thin permeable cell wall- for entry of water and ions
3. Cytoplasm contain extra mitochondria to provide the energy needed for active transport.

Question 12

Describe how guard cells are specialised for their funciton

Answer 12

Function- control the release and entry of gases.
Structure:
1. Found in pairs with a gap between them to form a stoma- necessary for CO2 to enter plants
2. One side of the cell wall is thicker than the other- In the light, guard cells take up water into their vacuoles and become turgid- thin outer walls and thickened inner walls force them to bend outwards, opening the stomata.
3. When they lose water- less swollen- change shape and stoma close to prevent further water loss.

Question 13

State the 4 main categories of tissues in animals.

Answer 13

1. Nervous tissue- adapted to support transmission of electrical impulses
2. Epithelial tissue- adapted to cover body surfaces, internal and external
3. Muscle tissue- adapted to contract
4. Connective tissue- adapted either to hold other tissues together or as a transport medium.

Question 14

Describe how squamos epithelium tissues are specialised for their function

Answer 14

1. Made of specialised squamous epithelial cells
2. Very thin (contains flat cells) and is one cell thick- allow efficient diffusion
3. Present when rapid diffusion across a surface is essential.
4. Forms lining of lungs and allows rapid diffusion of O2 into blood

Question 15

Describe how Ciliated epithelium are specialised for their function

Answer 15

1. Made of ciliated epithelial cells
2. Have hair like structures- cilia- which move in rhythmic manner
3. Line the trachea- cause mucus to be swept away from the lungs
4. Goblet cells are present- release mucus to trap unwanted particles present in the air and stops them reaching the lungs

Question 16

Describe how cartilage is specialised for its function

Answer 16

1. Connective tissue found in ears, nose and ends of bones.
2. Contains fibres of the proteins elastin and collagen.
3. It is a firm, flexible connective tissue composed of chondrocyte cells embedded in extracellular matrix.
4. Prevents the ends of bones from rubbing together and causing damage.

Question 17

Describe how muscle is specialised for its function

Answer 17

1. shortens in length in order to move bones which move different pars of the body.
2. Skeletal muscle fibres- attach to bone and contain myofibrils which contain contractile proteins.
3. There are different types of muscle fibres

Question 18

Describe how the epidermis of plants is specialised for its function

Answer 18

1. A single layer of closely packed cells covering the surface of plants
2. Usually covered by a waxy waterproof cuticle- reduces loss of water
3. Stomata are present in the epidermis- allow exchange of gases

Question 19

Describe how the xylem vessel is specialised for its function

Answer 19

1. Transports water and minerals around the plant
2. The walls of the cells are strengthened with waterproof lignin- provides structural support
3. Contains hollow xylem vessels which are elongated dead cells.
4. Contains parenchyma cells- fill in gaps between vessels.

Question 20

Describe how the phloem is specialised for its function

Answer 20

1. Transports organic nutrients- sucrose from leaves and stems to everywhere
2. Composed of columns of sieve tube cells separated by perforated walls called sieve plates- so sap can move easily through them
3. Also have companion cells linked to by plasmodesmata- perform all the cellular reactions of the sieve tube cells i.e have lots of mitochodira to provide ATP
4. Substances can move easily through the sieve tubes element because they have very little cytoplasm and thin cell walls

Question 21

State 3 examples of organ systems in animals and for each describe their function.

Answer 21

1. Digestive system- breaks down large insoluble molecules to small soluble ones, absorbs nutrients into blood, retains water and remove undigested material
2. Cardiovascular system- Moves blood around the body
3. Gaseous exchange system- brings air into body so oxygen an be extracted for Respiration and CO2 can be expelled

Question 22

Define stem cell

Answer 22

Undifferentiated cells with the potential to differentiate into a variety of the specialised cell types of the organism

Question 23

Define undifferentiated

Answer 23

An unspecialised cell originating from mitosis or meiosis

Question 24

Define totipotent

Answer 24

A stem cell that can differentiate into any type of cell and form a whole organisms

Question 25

Define pluripotent

Answer 25

A stem cell that can differentiate into any type of cell, but not form a whole organism

Question 26

Define multipotent

Answer 26

A stem cell that can only differentiate into a range of cell types within a certain type of tissue

Question 27

Define embryonic stem cell

Answer 27

A stem cell found within an embryo. Zygotes and the cells of the very early embryos are totipotent. When the embryo has developed into the blastocyst (a mass of cells) they are now pluripotent, they remain like this until a dew days before birth.

Question 28

Define tissue stem cell.

Answer 28

Found in specific areas e.g. bone marrow.
They are multipotent but might be able to be artificially triggered to become pluripotent?
They are how specialised tissues replace cells

Question 29

Describe the characteristic abilities of stem cells as compared to specialised cells.

Answer 29

1. Stems cells begin as undifferentiated cells and originate from meiosis or mitosis
2. They are unspecialised and have the potential to become any one of a range of specialised cell types in an organism
3. They are the source of new cells necessary for growth, development and tissue repair.

Question 30

Explain the importance of stem cells and why their activity must be carefully controlled.

Answer 30

1. If they don’t divide fast enough then tissues are not efficiently replaced- leading to ageing.
2. If there is uncontrolled division the they form masses of cells- tumours- lead to cancer

Question 31

State the 3 types of stem cell and give examples of where they occur in animals.

Answer 31

1. Totipotent- A fertilised egg or zygote and the 8 or 16 cells in the first stages of mitotic divisions.
2. Pluripotent- Present in early embryos and are the origin of the different types of tissue within an organism
3. Multipotent- Haematopoetic stem cells in bone marrow are multipotent- various types of blood cell

Question 32

State where stem cells occur in plants and state which type of potency they have.

Answer 32

1. stem cells are present in Meristematic tissue (meristems)- found wherever growth is occuring in the plants- tips of roots and shoots.
2. Meristematic tissue is also located between the xylem and phloem- vascular cambium- they’ll become cells in the phloem or xylem
3. Meristems are pluripotent

Question 33

Outline how a cell becomes specialised.

Answer 33

1. Certain conditions stimulate cells to differentiate into specialised
2. During differentiation certain genes are permanently switched off and some are switched on.
3. The genes which are switched on produce proteins and these proteins alter the metabolism and structure of the cell to make it specialised- often permanent change

Question 34

Where are erythrocytes and neutrophils are produced from

Answer 34

From stem cells in bone marrow which undergo differentiation.

Question 35

Explain why it is important for erythrocytes and neutrophils to be constantly produced.

Answer 35

1. Erythrocytes- lack of nucleus and organelles means they only have lifespan of around 120 days- need to be constantly replaced.
2. Neutrophils- They only live for around 6 hours so need to be replaced constantly

Question 36

List 7 diseases that stem cells have the potential to treat – for each describe how stem cells may be useful.

Answer 36

1. Heart disease- replace damaged muscle tissue after heart attack- normally irreparable
2. Type 1 diabetes- replace insulin producing cells
   which have been destroyed by the immune system
3. Parkinson’s- Replacing the dead dopamine-producing cells in the brain.
4. Alzheimer’s- replace brain cells which are destroyed by build up of abnormal proteins.
5. Macular degeneration- causes blindness in elderly and diabetics
6. birth defects
7. Spinal injuries- use stem cell implants in damaged spinal cords

Question 37

Describe how stem cells may be useful for treating burns.

Answer 37

1. Can be grown on biodegradeable meshes to produce new skin
2. Quicker than skin grafts

Question 38

Describe two ways in which stem cells may be useful in research.

Answer 38

1. They can divide indefinitely and differentiate into almost any cell within an organism

Question 39

Describe the arguments for and against the use of embryonic stem cells for research and medicine.

Answer 39

For:
1. Done well with regulation
2. Destroyed anyway
3. Relieve suffering
4. Help to stop the problem of the lack or organs for transplantation
Against:
1. Rights of embryo
2. Might lead to human cloning
3. May cause cancer if differentiation process is not able to be controlled
4. Goes against religious and cultural beliefs

Question 40

6. Define the term “induced pluripotent stem cell” and explain why they may be very useful in research and medicine.

Answer 40

A multipotent stem cell that has been chemically treated so that it reverts to a pluripotent state.