Unit 2.1 Producing New Cells

Question 1

Cell division (mitosis)

Answer 1

A single cell copies all its DNA and divides into 2 identical daughter cells.

Used to increase the number of cells in an organism.

Essential for growth and repair of tissues.

Question 2

Diploid

Answer 2

Body cells have 2 sets of chromosomes (one from each parent) so are said to be diploid.

The diploid number of chromosomes in human cells is 46.

Question 3

Chromosome complement

Answer 3

How many chromosomes there are in a cell.
There are 46 in a human cell.

Question 4

Haploid

Answer 4

Gametes contain one set of chromosomes (one from each pair) and are said to be haploid.

The haploid number of chromosomes in human gametes is 23.

Question 5

Replicated chromosome

Answer 5

A chromosome that has been copied before mitosis occurs.

Chromosomes must be copied so that new cells have a complete set of chromosomes containing the same DNA as the parent cell.

Replicated chromosomes are ‘X’ shaped and are made of 2 chromatids held together by a centromere.

The 2 chromatids are separated during mitosis, when the centromere splits.

Question 6

Centromere

Answer 6

Holds the 2 chromatids together in a replicated chromosome.

Question 7

Stages of mitosis

Answer 7

DNA is replicated and organised into chromosomes.

Chromosomes appear as they shorten and thicken, and the nuclear membrane breaks down.

Chromosomes line up on the equator of the cell and attach to spindle fibres.

Spindle fibres shorten, splitting the centromere and pulling the chromatids to opposite poles of the cell.

The chromosomes gather at the poles forming 2 new nuclei, with nuclear membranes.

The cytoplasm divides.

Question 8

Equator

Answer 8

An imaginary line along the misddle of a cell.
Replicated chromosomes line up here during mitosis.

Question 9

Spindle fibres

Answer 9

Used to separate daughter chromatids during mitosis.

Question 10

Chromatid

Answer 10

Replicated chromosomes are made of 2 daughter chromatids.

Chromatids are the 2 copies of the original DNA, which are separate during mitosis.

Chromatids are held together by a centromere.

Question 11

Meristem

Answer 11

The region of a plant where mitosis occurs.

Meristems are found at the root and shoot tip.

They are made of small, actively dividing, unspecialised cells.

These cells differentiate to form the specialised cell types found in plants.

Question 12

Stem cells

Answer 12

Unspecialised cells found in animals.

They are able to self-renew (copy themselves) and can develop into specialised cells.

Stem cells are used for growth and repair - all new body cells are produced from stem cells.

Question 13

Embryonic stem cells

Answer 13

Early embryos are made of a ball of embryonic stem cells.

They are able to copy themselves, and then can specialise into any type of cell needed to build a body.

Question 14

Tissue (adult) stem cells

Answer 14

Found throughout the body, throughout life.

Produce a limited range of cell types.

Used for growth, repair and renewal of cells in the tissues where they are found.

eg. bone marrow cells can only produce new blood cells.

Question 15

Therapeutic use of stem cells

Answer 15

Stem cells can be used to repair damaged or diseased organs or tissues by replacing cells.

Stem cells can be removed from embryos/adult tissues and can be cultured (grown) in a lab before being transplanted.

They can be used to produce new skin for skin grafts, and for producing new cells for corneal grafts (onto the eye).

Question 16

Research use of stem cells

Answer 16

Stem cells can be used to study cell processes, and to study how diseases such as cancer develop.

They can also be used for drug testing.

Question 17

Potential use of stem cells

Answer 17

How stem cells could be used in the future, eg. to replace damaged cells in organs such as the brain or heart.

Could be used to cure diseases such as heart disease, MS or Parkinson’s disease.

Question 18

Arguments in favour of the use of stem cells

Answer 18

They could be used to treat many diseases; the embryos used are ‘spare’ after IVF treatment and would be destroyed anyway; they can only be used up to 14 days old, so are not fully formed people.

Question 19

Arguments against the use of stem cells

Answer 19

Use of embryonic stem cells involves destruction of an embryo, which is a potential human life. Many people object on religious/moral grounds, and argue that it is unnatural.

Question 20

Specialised cells

Answer 20

Multicellular organisms are made of many specialised cells, which are adapted to carry out a particular function.

Stem cells differentiate and turn into specialised cells.

Examples of specialised cells include red blood cells, guard cells, root hair cells and neurons.

Question 21

Tissues

Answer 21

Specialised cells which group together to carry out a particular function. eg. muscle tissue is made of specialised muscle cells.

Question 22

4 main types of human body tissues

Answer 22

Epithelial (lining); connective (eg. tendons); muscle and nerve.

Question 23

Examples of plant tissues

Answer 23

Palisade and spongy mesophyll, xylem, phloem.

Question 24

Organs

Answer 24

Structures which are made of different tissues working together to carry out a particular function.

Organs can be made of several different types of tissue eg. the heart = muscle + connective tissue.

Question 25

Organ systems

Answer 25

Groups of organs that work together to carry out related functions eg. digestive system, nervous system