section 3: Reproduction and inheritance

Question 1

sexual reproduction: advantages

Answer 1

1) produces variation of offspring:
-this means that if the environment changes it is likely that an organism in the species will have a characteristic that allows them to survive (called a survival advantage)
-although some individuals may die, variation decreases the chance of the whole species becoming extinct
2) it allows us to use selective breeding:
-this type of reproduction mixes the genetic information from two organisms
-organisms with different desirable characteristics can be bred to produce offspring with even more desirable characteristics
-this speeds up natural selection
-an examples is to increase food production by breeding two animals with lots of meat

Question 2

asexual reproduction: advantages + what fertilisation is

Answer 2

-only one parent needed
-uses less energy and is faster as organisms do not need to find a mate
-in favorable conditions lots of identical offspring can be produced
-> fertilisation involves the fusion of a male and a female gamete to produce a zygote that undergoes cell division and develops into an embryo

Question 3

insect-pollinated flowers: adaptations

Answer 3

-petals: large and bright to attract insects
-nectar: scanted with nectar to attract insects
-pollen grains: sticky and in moderate amounts
-anthers: inside flower, stiff and attached so that insects can brush past
-stigma: inside flower, sticky so pollen grains stick to it when an insect brushes past

Question 4

wind-pollinated flowers: adaptations

Answer 4

-petals: small and dull-usually green and brown
-nectar: no scent or nectar
-pollen grains: smooth and light so they can easily be carried in the wind and in large amounts to make sure some reach other flowers
-anthers: outside flower, loose on long filaments so that pollen can be released easily
-stigma: outside flower, feather so forms network to catch pollen grains drifting in the wind

Question 5

seed and fruit formation:

Answer 5

-pollen grains are the male gamete in plants
-the ovule is the female gamete in plants
1) pollen grains land on stigma (via insect or wind pollination)
2) pollen tube grows out of the pollen grain and down the style into the ovary and then to the ovule
3) the male nucleus travels down the pollen tube from the pollen grain to fuse with the female egg nucleus in the ovule, forming a zygote
4) the zygote undergoes mitosis to form a seed
5) the ovule will become the seed and the ovule wall will become the seed coat
6) the ovary will become the fruit of the plant

Question 6

practical: understand the conditions needed for seed germination

Answer 6

-> germination is the process in which seeds begin to develop into a new young plant
-water: needed to activate enzymes to break down the starch food reserves in the seeds
-oxygen: needed for aerobic respiration to release energy for growth
-warmth: optinum temperature for enzymes will increase growth rate

Question 7

practical: understand the conditions needed for seed germination- actual practical

Answer 7

method:
1) set up 4 boiling tubes with 10 cress seeds in each, sitting on cotton wool
2) tube a should have dry cotton wool and kept at 20ºC
3) tube b should have moist cotton wool and kept at 20ºC
4) tube c should have boiled water that has been cooled, covered with a layer of oil and kept at 20ºC
5) tube d should have moist cotton wool but is kept at lower temperature (4ºC)
-the results will show that seeds germinate in test tube b only because it has the water, temperature and oxygen required for germination. tube a does not have water, the oil in tube c does not allow for oxygen and tube d is not kept at optimum temperature

Question 8

germinating seeds:

Answer 8

-embryo: young root and shoot become the adult plant
-food store: starch for the plant to use until it is able to carry out photosynthesis
-seed coat: a protective covering

Question 9

asexual reproduction:

Answer 9

-asexual reproduction produces clones as it only involved on parent, unlike sexual reproduction
natural: runners
-e.g. strawberry plants
-grow horizontally over soil surface and put down roots to form new plants
artificially: cuttings
-tissue samples scraped from parent plant and then placed in agar growth medium with nutrients and auxins
-the sample develop into plantlets and these are planted into compost to grow further

Question 10

male reproductive system:

Answer 10

-sex gland: produces semen that contains sperm cells
-sperm duct: sperm passes through this
-testis: contained in scrotum (bag of skin) and produces sperm and testosterone
-penis: passes urine and semen out of the body
-urethra: tube inside the penis to carry urine or semen, a ring of muscle inside stops the two mixing

Question 11

female reproductive system:

Answer 11

-ovary: contains ova (female gametes) which develop when FSH is released
-oviduct: connects ovary to the uterus and is lined with ciliated cells that push the ovum towards the uterus for fertilisation
-uterus: has a thick lining so that fertilised eggs can be implanted
-cervix: ring of muscle at lower end of uterus foetus remains in place during pregnancy
-vagina: muscular tube that leads to the inside of the body

Question 12

secondary sexual characteristics:

Answer 12

females: oestrogen
-breast development
-menstrual cycle begins
-growth of body hair
-widening of hips
-increased height
males: testosterone
-growth of penis and testes
-production of sperm
-growth of facial and body hair
-muscles development
-voice lowering and breaking

Question 13

menstrual cycle:

Answer 13

-the menstrual cycle lasts 28 days and the egg is usually released on day 14 (ovulation)
oestrogen:
-oestrogen causes thickening of the uterus in preparation for implantation of an egg
-levels peak on day 10 and then begin to fall
progesterone:
-progesterone mantains the thick lining of uterus
-inhibits the release of LH and FSH
-the egg matures on day 14 and progesterone starts increasing after this until it reaches its peak 3 days later
-if the egg is not fertlised progesterone levels fall and the uterus lining breaks down in a period that lasts for around 5 days

Question 14

developing an embryo:

Answer 14

-the placenta allows diffusion of glucose, oxygen and amino acids from the mother’s blood to the developing foetus for growth
-carbon dioxide and urea from the foetus are passed into the mother’s blood to be removed
-it also takes over the production of progesteron
-amniotic fluid is a liquid contained in a bag (amnion) in the uterus that surrounds the foetus
-it protects the foetus and cushions any rough movement
-when labour begins the amnion breaks and the fluid comes out-often known as a woman’s as a ‘water breaking’

Question 15

genetic definitions: gamete, genome, chromosome and gene

Answer 15

-gamete: an organism’s reproductive cell (egg in female and sperm in males), which has half the number of chromosomes (23)
-genome: the entire DNA of an organism
-chromosome: a structure found in the nucleus which is made up of a long strand of DNA
-gene: a short section of DNA that codes for a protein, and therefore contribute to a characteristic

Question 16

genetic definitions: alelle/variant, dominant allele and recessive allele

Answer 16

-allele/variant: the different forms of the gene-humans have two alleles for each gene as they inherit one from each parent
-dominant allele: only one (out of the two alleles) is needed for it to be expressed and for the corresponding the phenotype to be observed
-recessive allele: two copies are needed for it to be expressed and for the corresponding the phenotype to be observed
-homozygous: when both inherited alleles

Question 17

genetic definitions: homozygous and heterozygus

Answer 17

-homozygous: when both inherited alleles are the same (i.e. two dominant alleles or two recessive alleles)
-heterozygous: when one of the inherited alleles is dominant and the other is recessive

Question 18

genetic defitions: genotype and phenotype

Answer 18

-genotype: the combination of alleles an individual has, e.g. Aa
-phenotype: the physical characteristics that are observed in the individual, e.g. eye colour

Question 19

punnett square diagrams:

Answer 19

• a single gene cross looks at the probability of the offspring of two parents having certain genotypes and phenotypes
  -this is done using the alleles the two parents have for a gene and a punnet square diagram
  -describes monohybrid inheritance (looking at only one charactersitics, e.g. eye colour)
  -however, it is important to remember that most phenotypic features are the result of multiple different genes interacting rather than a single gene inheritance
  -uppercase letters are used to represent dominant characteristics
  -lowercase letters represent recessive characteristics, letters are usually A or B (can be whatever)

Question 20

sex determination:

Answer 20

-human body cells have 23 pairs of chromosomes:
-22 control characteristics, and the chromosomes in each pair look very similar
-the 23rd pair carries sex determining genes, and the two chromosomes can look different to each other (Y chromosomes are much smalles than X chromosome)
-the two possible chromosomes in the 23rd pair are X chromosomes and Y chromosomes
-when cells undergo meiosis to form a gamete, one sex chromosome goes into each gamete
-female have two X chromosomes, so therefore only pass on X chromosomes in their eggs
-males have one X chromosome and one Y chromosome, so therefore can pass on X or Y chromosomes in their sperm

Question 21

mitosis:

Answer 21

-> mitosis is a type of cell division where one cell divides to form two identical daughter cells
-the cell cycle is a series of steps that the cell has to undergo in order to do this
-cell division by mitosis occurs during growth and development, replacing damaged cells and also cloning
-mitosis is also a vital part of asexual reproduction, as this type of reproduction only involved one organism so to produce offspring it simply replicates its own cells

Question 22

mitosis: method

Answer 22

Stage 1 (interphase):
-the cell grows as organelles (such as ribosome and mitochondria) grow and increase in number
-the synthesis of protein occurs
-all 46 chromosomes are replicated (forming the characteristic ‘X’ shape)
-energy stores are increased
Stage 2:
-the chromosomes line up at the equator of the cell
-spindle fibres pull each chromosome of the ‘X’ to either side (poles) of the cell
Stage 3:
-two identical daughter cells form when the cytoplasm and cell membranes divide, each containing the same 46 chromosomes as the orginal cell

Question 23

meiosis:

Answer 23

-> meiosis is the formation of four non-identical cells from one cell
-cells in the reproductive organs divide by meiosis to form gametes
-gametes only have one copy of each chromosome

Question 24

meiosis: method

Answer 24

1) the cell makes copies of its chromosomes, so it has double the amount of genetic information
2) the cell divides into two cells, each with half the amount of chromosomes, giving the normal amount of 26 chromosomes (diploid)
3) each cell divides into two again to produce four cells, each with 23 chromosomes. As they have half of the normal amount of chromosomes they are called haploid
-these cells are called gametes and they are all genetically different from each other because the chromosomes are shuffed during the process, resulting in random chromsomes ending up in each of the four cells

Question 25

variation:

Answer 25

-genetic variation: is the difference in DNA sequences of individuals within the same species
-random fertilisation: increases genetic variation between offspring as each gamete has variation due to meiosis and the fusing of the egg and sperm is random
-genetic variation: would be eye colour, blood type etc as these phenotypes are dependent on inheriting alleles from parents
-environmental variation: is caused by differences in lifestyle, diet, climate etc. which could lead to organisms to adapt. An examples of this would be how white moths adapted to darker in more polluted areas
-genetics and environment: can interact, such as with height. A child might have the potential to grow tall, due to their genetics, but if they are malnourished and do not well or enough then they will not grow as much
-mutations are rare, random change in genetic material that can be inherited

Question 26

Darwin:

Answer 26

-evolution: a change in the inherited charactersitics of a population over time through a process of natural selection which may result in the formation of a new species
-natural selection: the process by which new species arise from existing species

Question 27

Darwin: mutations

Answer 27

-mutations occur which provide variation between organisms
-if a mutation provides a survival advantage the organism is more likely to survive to breeding age (survival of the fittest)
-the mutation will then be passed onto offspring
-over many generations, the frequency of the mutation will increase within the population

Question 28

Darwin: population

Answer 28

-within a population there is usually a large amount of genetic variation between individuals of the same species
-this natural variation occurs through small mutations that have occurred throughout time
-for example, we can see that within a particular breed of dog there are slightly different coat colours and patternings due to random mutations
-this may cause one population of a species to become so different that they can no longer interbreed to to produce fertile offspring
-this means that they have become a new species, called speciation

Question 29

antibiotic resistance in bacteria:

Answer 29

-bacteria are organisms that reproduce at a very fast rate and therefore advantageous genes, such as those for antibiotic resistance, can become prominent within a population very quickly
-exposer to antibiotics creates a selection pressure, as those with antibiotic resistant genes survive and those without die
-as a result those with antibiotic resistance can reproduce and pass on the advantageous gene to their offspring and so the population of antibiotic resistant bacteria increases
-as an examples is the MRSA ‘superbug’ that is resistant to many different types of antibiotics, it is found in hospitals as it spreads when doctors and nurses move between different patients