L5th Biology Michaelmas Midterm Revision

What does DNA stand for?

Deoxyribonucleic acid

What are the complementary base pairings on DNA?

Adenine + thymine, cytosine + guanine

What is a polymer?

A molecule made up of many repeating subunits

What is the monomer of DNA?

A nucleotide

What are the bases of nucleotides bonded by?

Weak hydrogen bonds

What is the structure of DNA?

DNA is made up of two strands coiled to form a double helix

What does each individual nucleotide contain?

A deoxyribose sugar, phosphate group (molecule) and a base

Why is the strawberry crushed in the DNA extraction practical?

To break down the cell wall and increase the surface area

Why is detergent added in the DNA extraction practical?

To break down the cell membrane

Why is protease added in the DNA extraction practical?

To break down proteins in the cell membrane

Why is the mixture heated in a water bath in the DNA extraction practical?

To speed up the reaction (protease will be at optimum temperature to function)

Why is salt added in the DNA extraction practical?

To clump the DNA together

Why is filtering carried out in the DNA extraction practical?

To remove insoluble excess material

Why is ice cold ethanol added in the DNA extraction practical?

To precipitate the DNA to make it visible

Define genome

The entire DNA of an organism (contains 20,000 genes)

Define DNA

Deoxyribonucleic acid - polymer of nucleotides

Define nucleotide

Monomer of DNA - contains deoxyribose sugar, phosphate group and a base

Define base

Nitrogenous component of a nucleotide which bonds to another complementary base (connects the two strands of DNA together with a weak hydrogen bond)

Define gene

A small section of DNA that codes for one specific protein

Define chromosome

An independent length of DNA located in the nucleus

Define cell

The basic unit of life

Define nucleus

Controls the activities of the cell and contains the genetic information in the form of DNA

Where does transcription occur?

The nucleus

Where does translation occur?

At a ribosome in the cytoplasm

Where are proteins made?

In the ribosomes

Where is DNA found?

In the nucleus

What does RNA have instead of thymine?

Uracil

Is RNA single stranded or double stranded?

Single stranded

Define mutation

A rare, random change to an organism’s DNA base sequence

What happens if a mutation happens in a gene?

It produces a genetic variant

Give an example of a mutagen

Gamma rays, X-rays, UV rays, Benzene, carcinogens (e.g. tobacco)

What happens if there are mutations in the non-coding DNA?

RNA polymerase may not be able to bind, may bind but not very well or may bind more strongly with the non-coding region

Define sexual reproduction

The formation of offspring from 2 parents. There is a fusion of the male and female gametes during fertilisation. The offspring inherit a mixture of genes from both parents

Define asexual reproduction

The formation of offspring from 1 parent. The offspring are clones of the parent and each other

Name an advantage of asexual reproduction

No need to find a mate, rapid reproductive cycle, advantageous alleles/adaptations are passed on through generations

Name a disadvantage of asexual reproduction

No variation, whole population is susceptible to the same selection pressure (e.g. disease)

Name an advantage of sexual reproduction

Variation, evolution can occur

Name a disadvantage of sexual reproduction

Takes time and resources to find a mate, disadvantageous characteristics may arise, gametes must be made (meiosis)

What is the purpose of meiosis?

To form gametes

What does meiosis form?

4 genetically different haploid daughter cells

What conclusions did Mendel come to about hereditary units in plants?

Hereditary units were inherited from both parents, hereditary units could be dominant or recessive, the dominant hereditary unit was always expressed

What are Mendel’s hereditary units known as now?

Genes

Define alleles

Different versions of the same gene

Why did Mendel not get any credit for his work while he was alive?

The structure of DNA was not known

What is a karyotype?

The complete set of chromosomes in a cell, usually displayed as an organised picture of the chromosomes during cell division

Define genotype

The combination of alleles you carry for a particular gene

Define phenotype

The observable characteristic that results from the genotype

What is AA also called?

Homozygous dominant

What is Aa also called?

Heterozygous

What is aa also called?

Homozygous recessive

Define homozygous dominant

Two of the same alleles that are dominant (e.g. AA)

Define heterozygous

Two different alleles, a dominant and recessive (e.g. Aa)

Define homozygous recessive

Two of the same alleles that are recessive (e.g. aa)

Define monohybrid inheritance

The inheritance of traits controlled by a single gene

What can we use a Punnett square to predict?

The possible genotypes and phenotypes of offspring from a genetic cross

Define nitrates

Compounds of nitrogen and oxygen

Where are nitrates found?

Soil, water and foods (typically leafy greens)

Can plants use atmospheric nitrogen (gas) (N2)?

No

Can plants use nitrate ions dissolved in soil water (NO3-)?

Yes

What 3 key routes are nitrates made available to plants through?

Crop rotation, fertilisation, nitrogen-fixing bacteria

What is nitrogen fixation?

The conversion of atmospheric nitrogen N2 into usable ammonia NH3 or NH4+, done by nitrogen-fixing bacteria such as Rhizobia in legume root nodules

What is ammonification?

The release of nitrogen back into the soil as ammonia NH3 or ammonium ions NH4+ done by decomposers breaking down organic waste

What is nitrification?

The oxidisation of ammonium ions into nitrates (making nitrogen available for plant uptake) done by nitrifying bacteria

What does lightning convert?

Nitrogen into nitrates

What do decomposers do in the nitrogen cycle?

Decompose proteins and urea and turn them into ammonia

What does ammonia form?

Ammonium ions in solution that plants can use

What does nitrifying bacteria do?

Turn ammonia in decaying matter into nitrites and then into nitrates (NH4+ -> NO2- -> NO3-)

What does nitrogen-fixing bacteria do?

Turn atmospheric nitrogen into ammonia, which forms ammonium ions

What does denitrifying bacteria do?

Turns nitrates back into nitrogen gas (this is of no benefit to living organisms). Often found in waterlogged soils (NO3- -> N2)

Name an advantage of crop rotation

No need for fertilisation - this means there is no eutrophication and there is also economical benefit

What does photosynthesis do in the carbon cycle?

Transforms atmospheric carbon into biomass (the mass of living material in an organism)

What does respiration do in the carbon cycle?

Releases carbon as carbon dioxide

What does decomposition do in the carbon cycle?

Breaks down dead organic material, releasing carbon dioxide through respiration

What does combustion do in the carbon cycle?

Releases carbon trapped in fossil fuels (decayed plant and animal matter)

What do plants use carbon from CO2 for?

To make carbohydrates, fats and proteins

What is eutrophication?

The process by which a water body becomes overly rich with nutrients such as nitrogen