B5- Growth And Development Flashcards
What do nucleotides contain?
Each nucleotide contains a small molecule called a base.
How many bases does a DNA have?
DNA has four different bases;
- adenine (A)
- cytosine (C)
- guanine (G)
- thymine (T)
What is base pairings?
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.
What is a gene?
A gene is a section of DNA that contains the instructions for one particular protein.
How do cells make proteins?
Cells make proteins by joining amino acids together in a particular order.
How do the amino acids go together?
It’s the order of the bases in a gene that tells the cell in what order to put the amino acids together.
How many bases codes for one amino acid?
Each set of three bases (triplet) codes for one amino acid.
What are ribosomes?
Proteins are made in the cell cytoplasm by organelles called ribosomes.
How does information get from the DNA to ribosome?
To get information from the DNA to the ribosome, a copy of the DNA is made using a molecule called messenger RNA.
Describe messenger RNA?
It is very similar to DNA but much shorter and a single strand.
Describe the process of the messenger RNA?
- 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.
How do cells grow and repair??
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.
What is the first stage of cell division?
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.
What happens after the DNA splits?
- 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.
Mitosis- Cell division?
- 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.
What is a zygote?
During sexual reproduction, an egg and a sperm combine to form a new cell called a zygote.
How many chromosomes will the zygote have??
When the egg and sperm combines the zygote contains 46 chromosomes.
One set of 23 from each parent.
What is Meiosis?
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)
Meiosis- Gametes?
- 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.
What is phototropism?
Some parts of a plant can respond to light by growing in a certain direction.
What is positive and negative phototropism??
Shoots are positively phototropism- they grow towards light.
Roots are negatively phototropism - they grow away from light.
Positive phototropism??
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.
Negative phototropism??
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.
What are auxins?
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.
