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 the term “specialised”.

Answer 2

Having a particular structure to serve a specific function.

Question 3

Define the term ‘‘differentiation’’.

Answer 3

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

Question 4

Explain why multicellular organisms have specialised cells.

Answer 4

Because multicellular organisms have many different complex processes taking place constantly. As a result, some cells need to have a specific structure that allows them to carry out a specific function effectively.

Question 5

Draw label and annotate diagrams to show how erythrocytes are specialised for their function.

Answer 5

Function: Carry oxygen in blood.

• Biconcave disc shape which provides a large SA for gas exchange.
• They have no nucleus and very few organelle. This increases the space available for haemoglobin.
• They are flexible so they can squeeze through narrow capillaries.

Question 6

Draw label and annotate diagrams to show how neutrophils are specialised for their function.

Answer 6

Function: A type of white blood cell, important part of the immune system.

• They have a flexible shape which allows them to engulf foreign pathogens.
• Multi lobed nucleus that makes it easier for them to squeeze through gaps to get to the site of infections.
• Cytoplasm contains many lysosomes which break down the engulfed particles.

Question 7

Draw label and annotate diagrams to show how sperm cells are specialised for their function

Answer 7

Function: deliver genetic information to the female gamete.

• Have a flagellum which means they are capable of movement.
• They have lots of mitochondria to provide energy for swimming.
• Acrosome (part of the head) contains digestive enzymes. These are released to digest the protective layers around the ovum, allowing the sperm to penetrate.

Question 8

Draw label and annotate diagrams to show how palisade cells are specialised for their function.

Answer 8

Function: The site of photosynthesis.

• contain many chloroplasts that absorb large amounts of energy for photosynthesis.
• The cells are a rectangular box shape so they can be closely packed to form a continuous layer.
• Have thin cell walls to increase the rate of diffusion of CO2.

Question 9

Draw label and annotate diagrams to show how

root hair cells are specialised for their function.

Answer 9

Function: Absorb mineral ions and water from the soil.

• They have lots of root hairs which are long extensions of the cell and act to increase its SA to maximise uptake of water and mineral ions.
• Thin permeable cell wall for entry of water and ions.
• Cytoplasm contains extra mitochondria to provide the energy needed for active transport.

Question 10

5. Draw label and annotate diagrams to show how guard cells are specialised for their .

Answer 10

Function: Control whether the stomata or opened or closed for the release or entry of gases.

• They are found in pairs with gap between them to form a stoma, this is necessary for CO2 to enter the plant.
• 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 stoma. One side of the cell wall is thicker than the other.
• When they loose water they become less swollen and change shape and the stoma close to prevent further.

Question 11

State the 4 main categories of tissues in animals.

Answer 11

• Nervous tissue which is adapted to support transmission of electrical impulses.
• Epithelial tissue. Adapted to cover body surfaces, internal and external.
• Muscle tissue. Adapted to contract.
• Connective tissue. Adapted either to hold tissues together or as a transport medium.

Question 12

Draw label and annotate diagrams to show how squamous epithelium is specialised for their function (link structure to function using annotations).

Answer 12

• It is made up of specialised squamous epithelial cells.
• Very thin because it contains flat cells.
• Only one cell think.
• Present when rapid diffusion across a surface is essential.
• It forms lining of lungs and allows rapid diffusion of O2 into blood.

Question 13

Draw label and annotate diagrams to show how ciliated epithelium is specialised for their function (link
structure to function using annotations)

Answer 13

• Made of ciliated epithelial cells.
• Have hair-structures called cilia which move in a rhythmic manner.
• They line the trachea and cause mucus to be swept away from the lungs. Goblet cells are present to release mucus to trap unwanted particles, stopping them reaching the lungs.

Question 14

Draw label and annotate diagrams to show how cartilage is specialised for their function (link
structure to function using annotations).

Answer 14

• A connective tissue found in ears, nose, between bones and ends of bones.
• Contains fibres of the proteins elastin and collagen.
• It is a firm flexible connective tissue composed of chondrocyte cells embedded in extra cellular matrix.
• It prevents the ends of bones from rubbing together and causing damage.

Question 15

Draw label and annotate diagrams to show how
muscle is specialised for their function (link
structure to function using annotations).

Answer 15

• Muscles shortens in length in order to move bones which move different parts of the body.
• Skeletal muscle fibres which attach to bone and contain myofibrils which contain contractile proteins.

Question 16

Define the term “cell”.

Answer 16

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 multi-cellular.

Question 17

Define the term “tissue”.

Answer 17

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

Question 18

Define the term “organ”.

Answer 18

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

Question 19

Define the term “organ system”.

Answer 19

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

Question 20

Draw label and annotate diagrams to show how the epidermis of plants are specialised for their function (link structure to function using annotations).

Answer 20

• A single layer of closely packed cells covering the surface of plants.
• Usually covered by a waxy water proof cuticle; this reduces the loss of water.
• Stomata are present in epidermis to allow the exchange of CO2, O2 and water vapour.

Question 21

Draw label and annotate diagrams to show how xylem tissue are specialised for their function (link
structure to function using annotations).

Answer 21

• It transports water and minerals around the plant
• Supports the plant because the walls of the xylem vessels are strengthened with water proof lignin which provides structural support for the plants.
• Contains hollow xylem vessels which are elongated dead cells.
• Also contains living parenchyma cells, these fill in the gap between xylem vessels.

Question 22

Draw label and annotate diagrams to show how phloem tissues are specialised for their function.

Answer 22

• Transports organic nutrients like sucrose from leaves and stems to everywhere.
• Composed of columns of sieve tube cells separated by perforated walls called sieve plates. These allow sap to move easily between cells.
• Substances can move easily through the sieve tube element because they have very little cytoplasm. They also have very thin walls.
• They also have companion cells (linked to the sieve tube by plasmodesmata) which perform all the cellular reactions of the sieve tube i.e. they have lots of mitochondria to provide ATP for the sieve.

Question 23

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

Answer 23

• Digestive system; breaks down large insoluble molecules to small soluble ones, absorbs nutrients into blood, retains water, removes undigested material.
• Cardiovascular system; moves blood around the body.
• Gaseous exchange system; brings air into the body so oxygen can be extracted for respiration.

Question 24

Define stem cell.

Answer 24

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

Question 25

Define undifferentiated cell.

Answer 25

An unspecialised cell originating from mitosis or meiosis.

Question 26

Define totipotent.

Answer 26

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

Question 27

Define pluripotent.

Answer 27

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

Question 28

Define multipotent.

Answer 28

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

Question 29

Define embryonic stem cell.

Answer 29

A stem cell found within embryos. 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 few days before birth.

Question 30

Define tissue stem cell.

Answer 30

They are 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. (They can be harvested from umbilical cords.)

Question 31

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

Answer 31

STEM CELLS

• Stem cells begin as undifferentiated cells and originate from meiosis or mitosis.
• They are unspecialised and have the potential to become anyone of a range of specialised cell types; its function is not yet defined.
• They are the source of new cells, necessary for growth development and tissues repair.

Question 32

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

Answer 32

• If the stem cells don’t divide fast enough then tissues are not efficiently replaced, leading to ageing.
• However, if there is uncontrolled division then they form masses of cells (tumours) which can lead to cancer.

Question 33

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

Answer 33

1) Totipotent - a fertilised egg or zygote and the 8 or 16 cells in the first stage of mitotic division.
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 so they can be differentiated to form different types of blood cell.

Question 34

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

Answer 34

• Meristematic tissues (meristems) have a lot of stem cells. They are found where ever growth is occuring in the plant i.e. the tips or roots and shoots.
• Meristematic tissue is also located between the xylem and the phloem. This is called the vascular cambium. They’ll differentiate to become cells in the xylem and phloem i.e. the companion cells.
• Meristems are pluripotent.

Question 35

Outline how a cell becomes specialised.

Answer 35

• Certain conditions stimulate cells to differentiate into specialised cells
• During the differentiation process certain genes are ‘switched off’ permanently and others are switched on.
• The genes which are switched on produce proteins and these proteins alter the metabolism and structure of the cell to make it specialised.
• This is often a permanent change.

Question 36

Where are enthrocytes and neutrophils produced from?

Answer 36

Stem cells in the bone marrow which undergo differentiation.

Question 37

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

Answer 37

• Erythrocytes: lack of nucleus and organelles means they only have a life span of around 120 days so they need to be constantly replaced.
• Neutrophils: They only live for around 6 hours so need to be replaced constantly.

Question 38

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

Answer 38

1) Heartdisease - replace damaged muscle tissue after heart attack (normally irreparable).
2) Type 1 diabetes - insulin producing cells which have been destroyed may be able to be replaced.
3) Parkinsons - replacing dead dopamine-producing cells in the brain to reduce symptoms of shaking.
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 39

Describe how stem cells may be useful for treating burns.

Answer 39

• Can be grown on biodegradable meshes to produce new skin. This is quicker than grafts.

Question 40

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

Answer 40

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

Question 41

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

Answer 41

FOR:
- It can be done well with regulation within the public domaine
- They will be destroyed anyway
- The treatments can relieve suffering
- It can help to stop the problem of the lack of organs for transportation.
AGAINST:
- rights of embryo
- could lead to human cloning
- may cause cancer if we can’t control the differentiation process
- goes against certain religious and cultural beliefs.

Question 42

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

Answer 42

A multipotent stem cell that has been chemically treated so it reverts to a pluripotent state. Pluripotent cells can form any cell type in the organism.