Long processes

Question 1

Mitosis

Answer 1

1.The cell grows
2.The DNA replicates to form two copies of each chromosome. These copies are joined together at a single point (the centromere).
2. The nuclear membrane breaks down. The chromosomes line up across the centre of the cell, attached to special spindle fibres
3. The chromatids (copies of chromosomes) are pulled apart and move to opposite ends of the cell.
4. The cytoplasm and cell membrane divides to form two identical cells.

Question 2

Meiosis

Answer 2

1.
The DNA replicates to form two copies of each chromosome. These copies are joined together at a single point
2.
The nuclear membrane breaks down. The homologous pairs of chromosomes join together.
3.
The homologous pairs of chromosomes exchange sections of DNA. They then attach to the
spindle fibres in pairs, at the centre of the cell.
4.
The homologous pairs of chromosomes are pulled apart and move to opposite ends of the cell. The cell divides.
5.
The chromosomes line up along the centre of the cell, attached to the spindle fibres. The
chromatids separate and move to opposite ends of the cell. Each cell divides again.

Question 3

Plant fertilisation

Answer 3

1. In plants pollen grains are deposited onto the stigma.
2. The pollen grain normally grows a pollen tube which grows down through the style.
3. Enzymes are secreted at the tip of the tube which digest the tissues of the style.
4. When the tube reaches an ovule the male gamete travels through the tube entering the ovule through a small hole called the micropyle.
5. It then fuses with the female gamete (ovum) in the process of fertilisation.
6. The fertilised ovum divides by mitosis to form the embryo
7. The ovule develops in the seed into the fruit

Question 4

Transcription

Answer 4

1. The two strands of the DNA helix are unzipped by breaking the weak hydrogen bonds between base pairs via an enzyme.
2. The enzyme RNA polymerase attaches to the DNA just before the gene.
3. RNA polymerase moves along the DNA strand. Free RNA nucleotides are attracted to the exposed DNA strand nucleotides by complementary base pairing.
4. RNA polymerase then catalyses the formation of covalent bonds between the RNA nucleotides to form a strand of mRNA

Question 5

Translation

Answer 5

1. The mRNA strand travels through the cytoplasm and attaches to the ribosome.
2. Amino acids are brought to the ribosome by tRN
3. The tRNA contains an anticodon, which is complementary to the codon for an amino acid
4. The complementary anticodons pair up, so amino acids are brought to the ribosome in the correct order
5. The amino acids are joined to form a protein

Question 6

Cloning

Answer 6

Nucleaus taken from a cell of the animal to be cloned
An egg cell (nucleaus removed) is taken from another sheep
The DNA from the nucleaus is fused with the empty egg cell with an electric shock; simulating mitosis
The cell is placed inside a foster mother, which develops into a embryo