SB3a - How may a plant such as a strawberry reproduce asexually?
- By using specail stems called runners which grow out from the root of the plant.
- These can also provide water and nutrients to the daughter plant until it is well develpoed.
SB3a - In what 3 scenarios would an aphid decide to reproduce asexually rather than sexually?
- when they couldn't find a mate
- when they are very well adapted to a new environment
- when they needed to reproduce qucikly
SB3a - What are the advantages and disadvantages for asexual reproduction?
- Very quick and takes up very little energy
- No need to find a mate
- many identical offspring can be produced for well adapted organisms in an unchanging environment
- No variation meaning that if they are vulnerable to a disease there is a high risk of extinciton
SB3a - What are the advantages and disadvantages of sexual reproduction?
- Creates variation meaning that a species is more likely to survive a disaster.
- It also allows them to move to different environments
- Time consuming from fertilisation to birth
- mate required
- smaller number of offspring
SB3a - What is the difference asexual and sexual reproduciton?
- Sexual reproduction involves fertilisation of a female gamete by a male gamete (two organisms)
- Asexual reproduction only requires one parent anf the offspring is genetically identical to their parent
SB3a - What type of cell divison occurs in each type of reproduction?
- Sexual Reproduction uses Meiosis to produce gametes which fuse during fertilization
- Asexual reproduction uses mitosis to produce clones
SB3b - Define the term genome
The entire genetic material of an organism
SB3b - What is the term for a fertilised egg before and after cell division starts to occurs?
- Before: A zygote
- After: An embryo
SB3b - What makes gametes different to regular body cells?
They are haploid rather than diploid meaning that they contain 1 set of 23 chromosones.
SB3b - What process is used for division of gamete cells, and how does this differ from mitosis?
- The gamete 'making' cell is diploid.
- Once it has divided in the same way as it would in mitosis, it divides once more without replicating the DNA producing haploid daughter cells.
SB3c - Describe the hydrogen bonding between Adenine/Thymine and Guanine/Cytosine
- A/T form two hydrogen bonds while C/G form three hydrogen bonds.
- This explains why each of them have pairs and A can't bond with C for .
SB3c - Describe the lab extraction of a precipitate of peas DNA.
- We mash up some peas then put them into a beaker containg a solution of detergent and salt, then mix well.
- The detergent will break down the cell membranes to release the DNA
The salt will cause the DNA to clump together
- We then filter the mixture to get the froth and large, insoluble bits of cell out.
- Then, we gently add some ice-cold ethanol to the filtered mixture.
- The DNA will start to come out of the solution as it's not soluble in cold ethanol. It will appear as a stringy white precipitate, that can be fished out with a galss rod.
The salt will cause the DNA to clump together
SB3c - Describe the structure of DNA.
- A double helix structure with nuecloetides.
- Each nucleuotide contains a phosphate group and a sugar.
- This forms a sugar phosphate backbone.
- They also have bases which form complementary base pairs and joined together by weak hydrogen bonds.
- The bases are adenine guanine thymine and cytosine with A being complimentary to T and C being complimentary to G.
- The DNA forms a polymer because it is many nuceuotides joined together.
SB3c - How many genes do humans roughly have?
SB3c - What are starch, proteins and cellulose polymers of?
- P: Polymer of amino acids
- S: Polymer of glucose
- C: Polymer of glucose
SB3c - Describe how DNA strands are held together
Parts of DNA have very slight electrical charges - a slightly negatively charged part of one base attracts a slightly positive charged part of another base. This forms a weak force of attraction called a hydrogen bond.
SB3c - What is a gene and why do genes differ between people?
- The order of bases form a gene.
- Everyone has a slightly different order of bases (except identical twins) meaning that they all have different genesd.
- Since DNA and genes are passed down along family, this information can be used to find out if people are related.
SB3c - What is a gene?
A section of DNA that contains the code instructions for a protein
SB3d - Descibe the process of translation.
- Translation is the second stage of protien synthesis and follows transcription
- The mRNA attaches to ribocomes in the cytoplasm
- The ribosome moves along the mRNA three bases at a time (a triplet of bases is called a codon)
- At each codon, a complemantary tRNA molecule, the anticodon, (that codes for a specific amino acid) joins opposite to it.
- Eventually, all the amino acids join up to from a polypeptide chain
- This chain will then fold up to form a protein
SB3d - Describe the process of transcription.
- Transcription is the first stage of protien synthesis in which RNA is created inside the nucleus
- RNA polymerase attaches to the non-coding binding site of the DNA
- This causes the strands of DNA to unzip. One strand acts as a template.
- Complementary nucleotides attach to the template strand EXCEPT Instead of T attaching to A, Uracil attaches to A
- The nucleotides join up to form a polymer of mRNA (RNA Polymerase)
- The mRNA leaves the nucleus through nuclear pores
SB3e - Describe how different bases create different proteins
- A triplet of bases forms a codon.
- Each codon codes for a different amino acid.
- Different orders and collections of amino acids will form different proteins
SB3e - What is a mutation and what are the two types of causes for this?
- A mutation is a change in the sequence of bases in a gene.
- This can be caused by DNA not being copied properly or by enviromental factors (such as radiation)
SB3e - Where along a strand of DNA would a mutation be most harmful?
- In the non-coding site.
- This is because this site decides when proteins and processes should/should not take place.
- A mutation in this could lead to repeated rapid mitosis leading to a cancerous tumor, or a lack of a required protien.
SB3f - Describe's Mendel's observation and conclusion through his experiment about characteristics of tall and short plants.
After breeding tall and short plants together, he noticed that:
- In the first generation of offspring, all the plants were tall
- Despite having both tall parent plants, the second generation of offspring contained some plants that were short
- This meant that characteristics inherited by offspring are not just a blend of parent's characteristics
- Also that there were 'factors' (now know as alleles) which affect this outcome and that one was dominant over the other
SB3f - What were Mendel's laws of inheritance?
- Each gamete receives only one factor for a characteristic
- The version of a factor that a gamete receives is random and does not depend on the other factors in the gamete
- Some versions of a factor are more 'powerful' than others and always have an effect on the offspring
SB3f - Why was Mendel's work largely ignored?
- Scientists did not see how 'factors' could explain the many variations in characteristics
- It didn't fit with Darwin's theory of evolution
SB3g - How is an allele chosen to be visible in the phenotype?
- There are dominant alleles (represented by capital letters) and recessive alleles.
- In any heterozygous case, the dominant allele will be visible in the phenotype.
- The only way a recessive allele can be visible is if both alleles present are recessive.
SB3g - What is the difference between heterozygous and homozygous.
- Homozygous: Both the allelles are the same
- Heterozygous: Both the alleles are different
SB3g - What is the phenotype?
The physical characteristic
SB3g- What is a genotype?
The genetic material of an organism, represented by letters