What is meiosis?
Cell division that produces haploid cells - gametes
What are gametes?
What is asexual reproduction?
Reproduction from one parent resulting in identical children
What is sexual reproduction?
Reproduction from two parents where gametes are fused to produce children with genetic variation
What are the advantages of asexual reproduction?
It can produce lots of offspring very quickly (rapid reproductive cycle), so organisms can colonise areas quickly
Only one parent is needed, so organisms can reproduce when conditions are favourable
What are the disadvantages of asexual reproduction?
There is no genetic variation between offspring in the population, so whole populations are vulnerable
What are the advantages of sexual reproduction?
It creates genetic variation within the population, so different individuals have different characteristics. This protects populations and leads to natural selection
What are the disadvantages of sexual reproduction?
It takes longer and uses more energy than asexual reproduction, so organisms produce fewer offspring in their lifetime
It needs two parents to take place, posing problems for isolated organisms. Organisms may have to mate when they find a mate, regardless of the conditions
What happens in meiosis?
Two cell divisions producing four haploid cells from one diploid father cell. The four daughter cells have 23 chromosomes in humans. It is used for sexual reproduction and produces gametes.
What are the ‘units’ of DNA called?
Nucleotides. They chain together to form DNA, a polymer
What are the components of a nucleotide?
An organic base is bonded to a sugar-phosphate backbone, made up of a sugar and a phosphate molecule. The nucleotide is then bonded to another at complimentary bases with a hydrogen bond
What are the organic bases and their pairings?
Adenine (A) and Thymine (T)
Cytosine (C) and Guanine (G)
What is a chromosome?
A coiled up molecule of DNA, found in the nucleus
What is a gene?
A section of DNA that ‘codes’ for a particular protein
What is a genome?
All of an organism’s DNA
How would you extract DNA from a fruit?
Mash the fruit and put it into a beaker containing a solution of detergent and salt and mix. The detergent breaks down cell membranes and the salt makes the DNA stick together
Filter the mixture to get the froth and insoluble bits of cell out
Add some ice cold alcohol to the mixture. The DNA is not soluble in cold alcohol so will start to come out
What is a codon?
A combination of three bases that codes for one amino acid
Where does protein synthesis take place?
In the ribosome, found in the cytoplasm
Why can’t chromosomes leave the nucleus?
They are too big to get out and they need to be protected from chemical reactions in the cytoplasm
What happens in transcription?
The sequence of DNA that contains the gene is unzipped by an enzyme called helicase
An enzyme called RNA polymerase creates the complementary mRNA from the DNA template
The mRNA leaves the nucleus through nuclear pores
The RNA polymerase can make numerous copies of mRNA when the DNA is unzipped
How does RNA differ from DNA?
RNA is single stranded and contains the base U instead of T