B5- Growth And Development

Question 1

What do nucleotides contain?

Answer 1

Each nucleotide contains a small molecule called a base.

Question 2

How many bases does a DNA have?

Answer 2

DNA has four different bases;

• adenine (A)
• cytosine (C)
• guanine (G)
• thymine (T)

Question 3

What is base pairings?

Answer 3

The two strands are held together by the bases which always pair up in the same way.

It’s always A-T and C-G. This is base pairings.

Question 4

What is a gene?

Answer 4

A gene is a section of DNA that contains the instructions for one particular protein.

Question 5

How do cells make proteins?

Answer 5

Cells make proteins by joining amino acids together in a particular order.

Question 6

How do the amino acids go together?

Answer 6

It’s the order of the bases in a gene that tells the cell in what order to put the amino acids together.

Question 7

How many bases codes for one amino acid?

Answer 7

Each set of three bases (triplet) codes for one amino acid.

Question 8

What are ribosomes?

Answer 8

Proteins are made in the cell cytoplasm by organelles called ribosomes.

Question 9

How does information get from the DNA to ribosome?

Answer 9

To get information from the DNA to the ribosome, a copy of the DNA is made using a molecule called messenger RNA.

Question 10

Describe messenger RNA?

Answer 10

It is very similar to DNA but much shorter and a single strand.

Question 11

Describe the process of the messenger RNA?

Answer 11

• The two DNA strands unzip. A molecule of messenger RNA is made using one strand of the DNA as a template. Base pairings ensure its a correct match.
• The messenger RNA molecule moves out of the nucleus and joins with a ribosome in the cytoplasm.
• The job of the ribosome is to stick amino acids together in a chain to make a protein, following the order of bases in the messenger RNA.

Question 12

How do cells grow and repair??

Answer 12

The cells in your body divide to produce more cells. So your body can grow and replace damaged cells.

When cells grow and divide over and over again- this is the cell cycle.

Question 13

What is the first stage of cell division?

Answer 13

The cell has to copy everything it contains so when it splits in half the two new cells will contain the right amount of material.

The number of organelles increases during cell growth.

The chromosomes are copied so the cell has two copies of its DNA.

Question 14

What happens after the DNA splits?

Answer 14

• Molecule of DNA splits.
• Bases on free floating nucleotides pair up with matching bases on the DNA.
• Cross links form between the bases and the old DNA strands, and the nucleotides are joined together.
• So two molecules identical to the original one are formed.

Question 15

Mitosis- Cell division?

Answer 15

• The cell has two copies of its DNA all spread out in long strands.
• Before the cell divides the DNA forms X shaped chromosomes. Each “arm” of a chromosome is an exact duplicate of the other.
• The chromosomes then line up at the centre of the cell and cell fibres pull them apart. The two arms of each chromosome go to opposite ends of the cell.
• Membranes form around each of the sets of chromosomes. These become the nuclei of the two new cells.
• The cytoplasm divides.
• Now there is two new cells containing exactly the same DNA. They are genetically identical to each other and the parent.

Question 16

What is a zygote?

Answer 16

During sexual reproduction, an egg and a sperm combine to form a new cell called a zygote.

Question 17

How many chromosomes will the zygote have??

Answer 17

When the egg and sperm combines the zygote contains 46 chromosomes.

One set of 23 from each parent.

Question 18

What is Meiosis?

Answer 18

Meiosis involves two divisions. It produces new cells that only have half the original number of chromosomes.

In humans it only happens in the ovaries and testes. (Reproductive system)

Question 19

Meiosis- Gametes?

Answer 19

• As with mitosis before the cell starts to divide, it duplicates its DNA. One arm of each chromosome is an exact copy of the other arm.
• In the first division of meiosis the chromosomes pairs line up in the centre of the cell.
• The pairs are then pulled apart so each new cell only has one copy of each chromosome. Some of the fathers chromosomes and some of the mothers chromosome goes into each new cell.
• In the second division the chromosomes line up again in the centre of the cell. The arms of the chromosomes are pulled apart.
• You get four gametes each with only a single set of chromosomes in it.
• After two gametes join at fertilisation the zygote grows by repeatedly dividing by mitosis.

Question 20

What is phototropism?

Answer 20

Some parts of a plant can respond to light by growing in a certain direction.

Question 21

What is positive and negative phototropism??

Answer 21

Shoots are positively phototropism- they grow towards light.

Roots are negatively phototropism - they grow away from light.

Question 22

Positive phototropism??

Answer 22

Plants need sunlight for photosynthesis-

Without sunlight plants can’t photosynthesise and don’t produce the food they need for energy and growth.

Photosynthesis occurs mainly in the leaves - so it’s important for plant shoots which grow leaves to grow in the direction of the sun.

Question 23

Negative phototropism??

Answer 23

Plants need nutrients and water from the soil to grow. Phototropism means roots grow away from light down into the soil where they can absorb the water and nutrients the plant needs for healthy growth.

Question 24

What are auxins?

Answer 24

They are chemicals that control growth near the tips of shoots and roots.

Auxins are involved in the responses of plants to light, gravity and water.

Question 25

Where are auxins produced?

Answer 25

Auxins are produced in the tips and diffuse backwards to stimulate the cell elongation process. Which occurs in the cells just behind the tips.

Question 26

What happens if the tip of the shoot is removed?

Answer 26

If the tips of the shoot is removed no auxins are available and the shoot may stop growing.

Question 27

Describe the process of the auxins??

Answer 27

• When a shoot tip is exposed to light, more auxins accumulate on the side that’s in the shade then the side that’s in the light.
• This makes the cells elongate faster on the shaded side so the shoot grows towards the light.

Question 28

What are meristems?

Answer 28

In plants, the only cells that are mitotically active are found in plant tissues called meristems.

Question 29

Where are meristems found?

Answer 29

Meristems tissue is found in the areas of a plant that are growing such as roots or shoots.

Question 30

What do meristems produce?

Answer 30

They produce unspecialised cells that are able to divide and form any type of cells in the plant. These cells can divide and generate any type of cell for as long as the plant lives.

Question 31

What do the unspecialised cells become?

Answer 31

They can become specialised and form tissues like xylem and phloem.

These tissues can group together and form organs like leaves,roots, stems and flowers.

Question 32

How are plant clones made?

Answer 32

• A cutting is part of a plant that has been cut off.
• Cutting taken from an area of the plant that’s growing will contain unspecialised meristem cells which can differentiate to make any cells.
• This means a whole new plant can grow from the cutting which will be a clone of the parent plant.
• Gardeners take cutting from plants with desirable features so the clones will be identical to the parent.

Question 33

What is rooting powder?

Answer 33

If you stick cuttings in the soil they won’t always grow.

If you add rooting powder which contains plant hormones (auxins) they’ll produce roots rapidly and start growing as new plants.

This helps growers produce lots of clones of a good plant very quickly.

Question 34

What is differentiation?

Answer 34

The process of stem cells becoming specialised is called differentiation.

Question 35

How can cloning make stem cells?

Answer 35

• You remove the genetic material from an egg cell.
• A nucleus from a body cell of the adult your cloning is then inserted into the “empty” egg cell.
• Under the right conditions, the inactive genes in the nucleus of the body cell can be reactivated. So that an embryo forms.
• These cells can turn into any kind of cell.

Question 36

Describe a DNA?

Answer 36

A DNA molecule has two strands coiled together in the shape of a double helix.

Each strand is made up of small units called nucleotides.