Reproduction (Edexcel GCSE Biology)
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Define the term asexual reproduction.
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Define the term asexual reproduction.
Asexual reproduction is a reproductive process that only involves one parent and that results in genetically identical offspring.
What are the advantages of asexual reproduction?
Advantages of asexual reproduction include:
a fast reproductive cycle
there is no need to find a mate
a population can grow quickly in a suitable environment
True or False?
Asexual reproduction results in genetically varied offspring.
False.
Asexual reproduction results in offspring that are genetically identical to their parents.
What is the main disadvantage of reproducing asexually?
The main disadvantage of asexual reproduction is that offspring are genetically identical. A population of genetically identical individuals are less likely to be able to adapt to changes in the environment.
Define the term sexual reproduction.
Sexual reproduction is a reproductive process that involves the fusion of gametes from two parents and that produces genetically varied offspring.
Sexual reproduction results in genetically offspring, meaning that a population is more likely to be able to to changes in the environment. Energy requirements are higher, however, due to the need to find a .
Sexual reproduction results in genetically varied/different offspring, meaning that a population is more likely to be able to adapt/respond to changes in the environment. Energy requirements are higher, however, due to the need to find a mate.
Define the term meiosis.
Meiosis is a type of nuclear division that produces genetically different cells. The cells produced by meiosis are gametes (sex cells).
What is the role of meiosis?
The role of meiosis is to produce genetically varied gametes (sex cells) with half the normal chromosome number.
True or False?
Meiosis results in genetically identical cells.
False.
Meiosis results in genetically different cells.
What happens to the chromosome number during meiosis?
During meiosis the chromosome number is halved from diploid (46 in humans) to haploid (23 in humans). For this reason meiosis is known as reduction division.
Describe the daughter cells produced by meiosis.
The daughter cells produced by meiosis can be described as follows:
there are four daughter cells
the cells are genetically different
the cells are haploid
the cells are gametes
Why is meiosis crucial for sexual reproduction?
Meiosis is crucial because it ensures that gametes (sperm and egg cells) have half the chromosome number, allowing for the correct chromosome number after fertilisation.
How many daughter cells are produced during the process of meiosis?
Meiosis produces four daughter cells.
Give three differences between meiosis and mitosis.
Some key differences between meiosis and mitosis include:
Mitosis
Meiosis
Diploid daughter cells
Haploid daughter cells
Two daughter cells
Four daughter cells
Daughter cells are genetically identical
Daughter cells are genetically different
Used for growth, repair and asexual reproduction
Produces sex cells for sexual reproduction
Describe the structure of DNA.
DNA is a polymer that consists of two strands coiled around each other to form a double helix. The strands are held together by a series of paired bases.
True or False?
The base pairs in the DNA double helix are held together by strong covalent bonds.
False.
The DNA base pairs are held together by weak hydrogen bonds.
What is the name of the molecule shown?
The molecule shown is a nucleotide.
Define the term polymer.
A polymer is a large molecule made up of many repeating subunits. DNA is a polymer containing many repeating nucleotides.
What are the four nucleotide bases found in DNA?
The four nucleotide bases in DNA are:
A
T
C
G
Describe how bases pair together in DNA.
Bases in DNA pair together via complementary base pairing:
A pairs with T
C pairs with G
True or False?
Nucleotide base A pairs with G in DNA.
False.
A pairs with T in DNA base pairing.
Define the term genome.
The genome is all of the DNA that an organism has.
What is a gene?
A gene is a section of DNA which codes for a specific protein.
What additional steps are needed, beyond steps 1 and 2, to extract DNA from strawberries using the method shown?
Extracting DNA from strawberries involves the following steps beyond steps 1 and 2:
filter the mixture to remove large pieces of tissue
add ice-cold ethanol
observe DNA in the layer of precipitate that forms between the mixture and the ethanol
How do genes code for proteins? (Higher Tier Only)
Genes code for proteins as follows:
genes contain a specific sequence of DNA bases
the order of bases in the DNA determines the order of amino acids in a protein
True or False?
Proteins all fold into the same generic shape. (Higher Tier Only)
False.
Each type of protein folds into a different specific shape.
True or False?
Enzymes are proteins with a specific structure. (Higher Tier Only)
True.
Enzymes are proteins which fold to produce an active site with a structure that is complementary to a specific substrate.
Define the term protein synthesis. (Higher Tier Only)
Protein synthesis is the process by which proteins are made in a cell.
What are the two processes that occur during protein synthesis? (Higher Tier Only)
The two processes that occur during protein synthesis are:
transcription
translation
What takes place during transcription? (Higher Tier Only)
During transcription an mRNA strand that is complementary to the coding DNA of a gene is produced.
What is the role of RNA polymerase in transcription? (Higher Tier Only)
The role of RNA polymerase in transcription is to:
bind to the non-coding DNA at the start of a gene
produce a complementary mRNA strand (by joining RNA nucleotides together)
True or False?
Translation occurs inside the nucleus. (Higher Tier Only)
False.
Translation occurs on ribosomes in the cytoplasm.
Transcription occurs in the nucleus.
Describe the process of translation. (Higher Tier Only)
Translation can be described as follows:
mRNA attaches to a ribosome
mRNA is decoded to produce a chain of amino acids with a specific sequence
amino acids are linked together to form polypeptides
Define the term codon. (Higher Tier Only)
A codon is a triplet of mRNA bases that corresponds to a specific amino acid.
What is the role of tRNA in translation? (Higher Tier Only)
The role of tRNA is to transfer specific amino acids to the ribosome. The amino acid transferred is determined by the region of the tRNA called the anticodon, which binds to a complementary mRNA codon.
True or False?
During translation the amino acids are linked to form polysaccharides. (Higher Tier Only)
False.
During translation the amino acids are linked to form polypeptides.
What is a genetic variant? (Higher Tier Only)
A genetic variant is a change in the normal base sequence of DNA. Variants arise due to mutation.
What is non-coding DNA? (Higher Tier Only)
Non-coding DNA is DNA that is not part of a gene, so does not code for protein.
True or False?
Changes to non-coding DNA can affect phenotype. (Higher Tier Only)
True.
Changes to non-coding DNA can affect phenotype. Even though non-coding DNA does not code for proteins, changes in these regions can influence the transcription of coding DNA.
How can genetic variants in non-coding DNA influence protein synthesis? (Higher Tier Only)
Genetic variants in the non-coding DNA at the start of a gene can influence the binding of RNA polymerase; this may increase or decrease transcription of the gene, altering the quantity of protein synthesised.
How can genetic variants in coding DNA affect phenotype? (Higher Tier Only)
Genetic variants in non-coding DNA can affect phenotype as follows:
the DNA may code for a different amino acid
the resulting polypeptide will have a different amino acid sequence
the polypeptide may fold differently, resulting in a protein with altered function, e.g. an enzyme may have higher or lower activity levels