SB3 Flashcards Preview

Biology❌ > SB3 > Flashcards

Flashcards in SB3 Deck (58)
Loading flashcards...

What does sexual reproduction produce?

Genetically different cells.


How many chromosomes do gametes contain?

Only half the number of a normal cells.

They’re haploid


What is sexual reproduction?

1. It’s where genetic information from two organisms (a father and mother) is combined to produce offspring which are genetically different to either parent.

2. The father and mother produce gametes (reproductive cells). In animals these are sperm and egg cells.


What happens at fertilisation?

A male gamete fuses with a female gamete to produce a fertilised egg, also known as a zygote.

The zygote ends up with the full set of chromosomes (so its diploid).


What happens to the zygote after fertilisation?

It then undergoes cell division (by mitosis) and develops into an embryo.

The embryo inherits characteristics from both parents as it has received a mixture of chromosomes (and therefore genes)from its mum and dad.


What’s a gamete?

Reproductive cell.


What’s a diploid cell?

Has a full set of chromosomes.


What’s a haploid cell?

Have half the number of chromosomes of normal cells.


What’s a zygote?

Fertilised egg.


How are gametes produced?



What is meiosis?

It’s a type of cell division.
It doesn’t produce identical cells like mitosis does.


Explain what happens in the first division of meiosis

1. Before the cell starts to divide, it duplicates its DNA. One arm of each x shaped chromosome is an exact copy of the other arm.

2. The chromosomes line up in pairs in the centre of the cell. One chromosome in each pair came from the organisms mother and one came from its father.

3. The pairs are then pulled apart, so each new cell only has one copy of each chromosome. Some of the fathers and mothers chromosomes go into each new cell.

4. Each new cell will have a mixture of the mothers and fathers chromosomes. Mixing up the genes like this is really important - it creates genetic variation.


Explain what happens in the second division of meiosis

1. In the second division the chromosomes line up again in the centre of the cell. The arms of the chromosomes are pulled apart.

2. Your get four haploid daughter cells - these are gametes. Each gamete only has a single set of chromosomes. The gametes are all genetically different.


What happens when cells reproduce asexually?

They divide by mitosis - this results in two diploid daughter cells, which are genetically identical to each other and to the parent cell.


What are the advantages of asexual reproduction?

Can produce lots of offspring very quickly because the reproductive cycle is so fast.
This can allow organisms to colonise a new area very rapidly.

Only one parent is needed - this means organisms can reproduce whenever conditions are favourable without having to wait for a mate.


What are the disadvantages of asexual reproduction?

There’s no genetic variation between offspring in the population, so if the environment changes and conditions become unfavourable, the whole population may be affected.


What are the advantages of sexual reproduction?

Creates genetic variation within the population, which means different individuals have different characteristics.
This means that if the environmental conditions change, its more likely that at least some individuals will have the characteristics to survive.

Over time this can end to natural selection and evolution, as species become better adapted to their new environment.


What are the disadvantages of sexual reproduction?

Takes more time and energy than asexual, so organisms produce fewer offspring in their lifetime.

Two parents are needed for sexual reproduction. This can be a problem if individuals are isolated.


What is DNA made up of?



What is DNA?

Its strands of polymers made up of lots of repeating units called nucleotides.


What do nucleotides consist of?

One sugar molecule.
One phosphate molecule.
One base.


What do the sugar and phosphate molecules do?

They form a backbone to the DNA strands.
They alternate.


What are the different bases?

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


What shape is DNA?

Double helix.

Two strands coiled together in a spiral.


What do bases join to?

One of four different bases join to each sugar.
Each base links to a base on the opposite stand in the helix.

A always pairs up with T.
C always pairs up with G.


What are the base pairings called?

Complementary base pairing.


What are base pairings joined together by?

Weak hydrogen bonds.


What is DNA stored as?



What is a chromosomes?

Are long, coiled up molecules of DNA.


What is a gene?

Is a section of DNA on a chromosome that codes for a particular protein.