chapter 6 p3

Question 1

What is a Tissue:

Answer 1

A tissue is made up of a collection of differentiated cells that have a specialised function or functions.
As a result, each tissue is adapted for a particular function within the organism

Question 2

There are four main categories of tissues in animals:

Answer 2

nervous tissue, adapted to support the 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 other tissues together or as a transport medium.

Question 3

Specialised animal cells:
Squamous epithelium:

Answer 3

made up of specialised squamous epithelial cells, is sometimes known as pavement epithelium due to its flat appearance.
It is very thin due to the squat or flat cells that make it up and also because it is only one cell thick.
It is present when rapid diffusion across a surface is essential. It forms the lining of the lungs and allows rapid diffusion of oxygen into the blood.

Question 4

Ciliated epithelium:

Answer 4

is made up of ciliated epithelial cells.
The cells have ‘hair-like’ structures called cilia on one surface that move in a rhythmic manner.
Ciliated epithelium lines the trachea, for example, causing mucus to be swept away from the lungs.
Goblet cells are also present, releasing mucus to trap any unwanted particles present in the air.
This prevents the particles, which may be bacteria, from reaching the alveoli once inside the lungs.

Question 5

Cartilage:

Answer 5

is a connective tissue found in the outer ear, nose and at the ends of (and between) bones.
It contains fibres of the proteins elastin and collagen.
Cartilage is a firm, flexible connective tissue composed of chondrocyte cells embedded in an extracellular matrix.
prevents the ends of bones from rubbing together and causing damage.
Many fish have whole skeletons made of cartilage, not bone.

Question 6

Muscle:

Answer 6

is a tissue that needs to be able to shorten in length (contract) in order to move bones, which in turn move the different parts of the body.
There are different types of muscle fibres.
Skeletal muscle fibres (muscles which are attached to bone) contain myofibrils (dark pink bands on the micrograph) which contain contractile proteins.
The skeletal muscle micrograph shown here has several individual muscle fibres (pink) separated by connective tissue (thin white strips).

Question 7

There are a number of different tissues in plants, including

Answer 7

epidermis tissue, adapted to cover plant surfaces
vascular tissue, adapted for transport of water and nutrients.

Question 8

examples of specialised tissues in plants:
The epidermis:

Answer 8

is a single layer of closely packed cells covering the surfaces of plants.
It is usually covered by a waxy, waterproof cuticle to reduce the loss of water.
Stomata, formed by a pair of guard cells that can open and close are present in the epidermis.
They allow carbon dioxide in and out, and water vapour and oxygen in and out.

Question 9

Xylem tissue:

Answer 9

is a type of vascular tissue responsible for transport of water and minerals throughout plants.
The tissue is composed of vessel elements, which are elongated dead cells.
The walls of these cells are strengthened with a waterproof material called lignin (pink rings in the micrograph), which provides structural support for plants.

Question 10

Phloem tissue:

Answer 10

is another type of vascular tissue in plants, responsible for the transport of organic nutrients, particularly sucrose, from leaves and stems where it is made by photosynthesis to all parts of the plant where it is needed.
It is composed of columns of sieve tube cells separated by perforated walls called sieve plates.

Question 11

What is an Organ:

Answer 11

An organ is a collection of tissues that are adapted to perform a particular function in an organism.
For example, the mammalian heart is an organ that is adapted for pumping blood around the body.
It is made up of muscle tissue and connective tissue.
The leaf is a plant organ that is adapted for photosynthesis. It contains epidermis tissues and vascular tissue

Question 12

Organ systems:

Answer 12

Large multicellular organisms have coordinated organ systems.
Each organ system is composed of a number of organs working together to carry out a major function in the body.

Question 13

Animal examples of organ systems include:

Answer 13

the digestive system, which takes in food, breaks down the large insoluble molecules into small soluble ones, absorbs the nutrients into the blood, retains water needed by the body and removes any undigested material from the body
the cardiovascular system, which moves blood around the body to provide an effective transport system for the substances it carries
the gaseous exchange system, which brings air into the body so oxygen can be extracted for respiration, and carbon dioxide can be expelled.

Question 14

differentiation.

Answer 14

The process of a cell becoming specialised
involves the expression of some genes but not others in the cell’s genome.

Question 15

Stem cells

Answer 15

All cells in plants and animals begin as undifferentiated cells and originate from mitosis or meiosis.
They are not adapted to any particular function (they are unspecialised) and they have the potential to differentiate to become any one of the range of specialised cell types in the organism.
These undifferentiated cells are called stem cells.
Stem cells are able to undergo cell division again and again, and are the source of new cells necessary for growth, development, and tissue repair.
Once stem cells have become specialised they lose the ability to divide, entering the G, phase of the cell cycle

Question 16

Why the activity of stem cells has to be strictly controlled:

Answer 16

If they do not divide fast enough then tissues are not efficiently replaced, leading to ageing.
However, if there is uncontrolled division then they form masses of cells called tumours, which can lead to the development of cancer.

Question 17

What is stem cell potency:

Answer 17

A stem cell’s ability to differentiate into different cell types is called potency.
The greater the number of cell types it can differentiate into, the greater its potency.
Stem cells differ depending on the type of cell they can turn into
Types of cell stem cells can turn into:
Totipotent
Pluripotent
Multipotent

Question 18

Totipotent

Answer 18

these stem cells can differentiate into any type of cell.
A fertilised egg, or zygote and the 8 or 16 cells from its first few mitotic divisions are totipotent cells, which are destined eventually to produce a whole organism.
They can also differentiate into extra-embryonic tissues like the amnion and umbilicus.

Question 19

Pluripotent

Answer 19

these stem cells can form all tissue types but not whole organisms.
They are present in early embryos and are the origin of the different types of tissue within an organism.

Question 20

Multipotent

Answer 20

these stem cells can only form a range of cells within a certain type of tissue.
Haematopoetic stem cells in bone marrow are multipotent because this gives rise to the various types of blood cell.

Question 21

Differentiation:

Answer 21

Multicellular organisms like animals and plants have evolved from unicellular (single-celled) organisms because groups of cells with different functions working together as one unit can make use of resources more efficiently than single cells operating on their own.
In multicellular organisms cells have to specialise to take on different roles in tissues and organs.
They may be required to form barriers such as skin or be motile such as sperm cells.
Cells have adapted to different roles in an organism and so have many shapes (and sizes) and often contain different organelles.

Question 22

Blood cells and their different functions:

Answer 22

Erythrocytes (red blood cells) and neutrophils (white blood cells) are both present in blood
They look very different because they have different functions.
When cells differentiate they become adapted to their specific role.
What form this adaptation takes is dependent on the function of the tissue, organ and organ system to which the cell belongs.
All blood cells are derived from stem cells in the bone marrow.

Question 23

Replacement of red blood cells:

Answer 23

Mammalian erythrocytes are essential for the transport of oxygen around the body.
They are adapted to maximise their oxygen-carrying capacity by having only a few organelles so there is more room for haemoglobin.
Due to the lack of nucleus and organelles they only have a short lifespan of around 120 days.
They therefore need to be replaced constantly.
The stem cell colonies in the bone marrow produce approximately three billion erythrocytes per kilogram of body mass per day to keep up with the demand.

Question 24

Replacement of white blood cells:

Answer 24

Neutrophils have an essential role in the immune system.
They live for only about 6 hours and the colonies of stem cells in bone marrow produce in the region of 1.6 billion per kg per hour.
This figure will increase during infection.

Question 25

Sources of animal stem cells

Answer 25

Embryonic stem cells

Tissue (adult) stem cells

Question 26

Embryonic stem cells

Answer 26

these cells are present at a very early stage of embryo development and are totipotent.
After about seven days a mass of cells, called a blastocyst, has formed and the cells are now in a pluripotent state.
They remain in this state in the fetus until birth.

Question 27

Tissue (adult) stem cells

Answer 27

these cells are present throughout life from birth.
They are found in specific areas such as bone marrow.
They are multipotent, although there is growing evidence that they can be artificially triggered to become pluripotent.
Stem cells can also be harvested from the umbilical cords of newborn babies.
The advantages of this source are the plentiful supply of umbilical cords and that invasive surgery is not needed.
These stem cells can be stored in case they are ever needed by the individual in the future, and tissues cultured from such stem cells would not be rejected in a transplant to the umbilicus’ owner.

Question 28

Sources of plant stem cells:

Answer 28

Stem cells are present in meristematic tissue (meristems) in plants.
This tissue is found wherever growth is occurring in plants, for example at the tips of roots and shoots (termed apical meristems).
Meristematic tissue is also located sandwiched between the phloem and xylem tissues and this is called the vascular cambium.
Cells originating from this region differentiate into the different cells present in xylem and phloem tissues
In this way the vascular tissue grows as the plant grows.
The pluripotent nature of stem cells in the meristems continues throughout the life of the plant.

Question 29

Uses of stem cells:
Stem cells transplanted into specific areas have the potential to treat certain diseases, such as:
p1

Answer 29

heart disease - muscle tissue in the heart is damaged as a result of a heart attack, normally irreparably - this has been tried experimentally with some success already
type 1 diabetes - with insulin-dependent diabetes the body’s own immune system destroys the insulin-producing cells in the pancreas; patients have to inject insulin for life - this has been tried experimentally with some success already
Parkinson’s disease - the symptoms (shaking and rigidity) are caused by the death of dopamine-producing cells in the brain; drugs currently only delay the progress of the disease

Question 30

Stem cells transplanted into specific areas have the potential to treat certain diseases, such as:
p2

Answer 30

• Alzheimer’s disease - brain cells are destroyed as a result of the build up of abnormal proteins; drugs currently only alleviate the symptoms
• macular degeneration, - this condition is responsible for causing blindness in the elderly and diabetics; scientists are currently researching the use of stem cells in its treatment and early results are very encouraging
• birth defects - scientists have already successfully reversed previously untreatable birth defects in model organisms such as mice.
• spinal injuries - scientists have restored some movement to the hind limbs of rats with damaged spinal cords using stem cell implants.

Question 31

Stem cells are already used in such diverse areas as:

Answer 31

• the treatment of burns - stem cells grown on biodegradable meshes can produce new skin for burn patients, this is quicker than the normal process of taking a graft from another part of the body
• drug trials - potential new drugs can be tested on cultures of stem cells before being tested on animals and humans
• developmental biology - with their ability to divide indefinitely and differentiate into almost any cell within an organism, stem cells have become an important area of study in developmental biology.
• This is the study of the changes that occur as multicellular organisms grow and develop from a single cell, such as a fertilised egg - and why things sometimes go wrong.

Question 32

Ethics: p1
Evolution of Embryonic Stem Cell Use:

Answer 32

More recently, the use of embryonic stem cells in therapies and research has lead to controversy and debates regarding the ethics of such use.
The embryos used originally were donated from those left over after fertility treatment.
More recently the law in the UK has changed so that embryos can be specifically created in the laboratory as a source of stem cells.

Question 33

Ethics: p2
Ethical Concerns and Legal Shifts:

Answer 33

The removal of stem cells from embryos normally results in the destruction of the embryos, although techniques are being developed that will allow stem cells to be removed without damage to embryos.
There are not only religious objections to the use of embryos in this way but moral objections too - many people believe that life begins at conception and the destruction of embryos is, therefore, murder.
There is a lack of consensus as to when the embryo itself has rights, and also who owns the genetic material that is being used for research.
This controversy is holding back progress that could lead to the successful Treatment of many incurable diseases.

Question 34

ethics p3 Alternatives and Advancements in Stem Cell Research:

Answer 34

The use of umbilical cord stem cells overcomes these issues to a large extent, but these cells are merely multipotent, not pluripotent like embryonic stem cells, thus restricting their usefulness.
Adult tissue stem cells can also be used but they do not divide as well as umbilical stem cells and are more likely to have acquired mutations.
Developments are being made towards artificially transforming tissue stem cells into pluripotent cells.
Induced pluripotent Stem cells (iPSCs) are adult stem cells that have been genetically modified to act like embryonic stem cells and so are pluripotent.
The use of plant stem cells doesn’t raise the same ethical issues as animal cells

Question 35

Gene therapy using stem cells: p1

Overview of Severe Combined Immunodeficiency (SCID)

Answer 35

Children born with the rare genetic condition Severe Combined Immunodeficiency (SCID) are extremely vulnerable to all infections and without treatment are unlikely to live for more than a year.
They produce no T cells, and without T cells the B cells do not function either (T cells and B cells are types of white blood cell).

Question 36

Gene therapy using stem cells: p2
Traditional Treatment and Challenges

Answer 36

Normally SCID is treated with a bone marrow transplant, which depends on finding a matching donor.
The transplanted stem cells divide and differentiate into the different types of white blood cells needed for a healthy immune system.

Question 37

Gene therapy using stem cells: p3
Gene Therapy Innovations and Challenges

Answer 37

More recently experimental gene therapy has been used to treat SCID.
The aim is that stem cells from the patient’s own bone marrow are removed and genetically modified so that they function normally to produce the white blood cells needed.
These are then put back into the patient and the condition should be corrected.
This treatment was initially successful in a small number of children, but in some of the children another gene was damaged in the process and they went on to develop leukaemia.
However, gene therapy is still seen as having the most potential for treating SCID in the future.

Question 38

Plant stem cells and medicines:

Answer 38

Plant stem cells have a huge potential role to play in medicine.
Many drugs used in medicines are derived from plants.
Plant stem cells can be cultured, leading to an unlimited, and cheap, supply of plant-based drugs.

Question 39

Example of plant stem cell:

Answer 39

Paclitaxel is a common drug used in the treatment of breast and lung cancer.
It cannot be chemically synthesised and must be obtained from the bark of yew trees (Taxus brevifolia).
The trees have to be mature, which means the supply is limited and the extraction process difficult and expensive.
An alternative way of producing the drug was developed using a related plant but it is still a difficult and expensive process.
Recently Stem cells from the yew tree have been used to produce paclitaxel cheaply and in sustainable quantities.