reproduction + inheritance

Describe the features of an insect pollinated flower that helps it attract insects

- Large petals - attract insects

- Coloured petals - attract insects

- Scent - makes insects push past stamen

- Nectar - makes insects push past stamen

- Sticky pollen grains - attach to insect

Describe the features of a wind pollinated flower

• Exposed stamens - allows pollen grains to be easily released

• Feathery stigma - catches drifting pollen grains

• Small petals - allows stamens and stigmas to be exposed

• Small pollen grains - easily carried by the wind

Describe the events that lead to seed formation

• Pollen lands on stigma

• Pollen tube grows down style into ovary

• Male gamete (pollen) fuses with female gamete (egg)

• Ovule => seed

• Ovule wall => seed coat

• Ovary => fruit

Describe the structure of a seed

Plumule

Padicle

Cotyledon (Food store)

Testa (Seed coat)

What is germination?

• Food store in seed is used up

• Radicle grows down

• Plumule grows up towards light and starts photosynthesis

What conditions are needed for germination?

• Water - to activate enzymes

• Oxygen - for respiration

• Warm temperature - optimum temp for enzyme controlled reactions

Describe an investigation into the factors required for germination

• Set up 4 test tubes, each containing 15 seeds on cotton wool

  • In one test tube (A) leave cotton wool dry

  • In one test tube (B) add water to cotton wool, to make it moist

  • In one test tube (C) add water to cotton wool, then add a later of oil on top to prevent oxygen diffusion to the seeds

  • In one test tube (D) add water to the cotton wool to make it moist, then place it in the fridge

  • Leave tubes A B and C at room temperature

  • Leave all tubes for a set period of time, like 5 days

  • Compare results and see which tube has the greatest number of germinated seeds

Which test tube would you expect to see the greatest number of seeds germinating?

• B

  • only tube providing water, oxygen and warmth

  • all others missing at least one vital factor

Give the independent variable for this investigation?

Number of seeds germinating after 5 days

Give control variables for this investigation

• Temperature of tubes A B C

• Species of cress seeds used

• Parent plant of cress seeds

• Type of water used (boil first and then cool)

• Light intensity

Give examples of natural asexual reproduction in plants

• Strawberry runners

• Tubers

Describe how strawberry runners reproduce asexually

• Runners = horizontal stems growing sideways from parent plant

• When runners touch the soil, plantlets grow roots

• New plantlets grow and become independent from parent plant

Give an example of an artificial method of asexual reproduction in plants

• Taking a cutting

Describe the process of taking a cutting

• A piece of a plants stem is cut off

• Dipped in rooting powder with plant growth hormones

• Transferred to soil

• Grow into genetically identical plants

penis

- Passes urine out of the body from the bladder

- Allows semen to enter into the vagina of a woman during sexual intercourse

Testis

- Contained in the scrotum

- Produces sperm and testosterone

Sperm Duct

• Sperm passes through the sperm duct where it mixes with fluids produced by the sex gland

Sex gland

Produces semen - provides sperm cells with nutrients

Urethra

Exports urine or semen from the body

Ring of muscle in the urethra prevents mixing of urine and semen

Where is testosterone made and what is its function?

Testes

Stimulates secondary sexual characteristics like voice deepening, sperm production, pubic hair

Oviduct

• Connects the ovary with the uterus

• Lined with cilated cells to push the ovum towards the uterus for fertilisation

Ovary

Contains female gametes (ova) which mature and develop when FSH is released

uterus

muscular structure with a soft lining

fertilised egg cell implanted there to develop into a foetus

Cervix

Ring of muscle at lower end of uterus

Keeps foetus in place during pregnancy

Urethra

Tube that passes urine out of the body

Vagina

Muscular tube that the male’s penis enters during sexual intercourse

How long does the menstrual cycle last

Approximately 28 days

On which day is the egg usually released

14

What is menstruation

Breakdown of the thickened uterus lining

Occurs when the egg has not been fertilised

How long does menstruation last

5-7 days

Where is oestrogen made and what is its function?

Ovaries

Stimulates secondary sexual characteristics - hips widening, breast growth, pubic hair

Causes thickening of uterus lining

Inhibits FSH and stimulates LH

Where is progesterone made and what is its function?

Initially corpus luteum, later in pregnancy the placenta

Maintains uterus lining

Inhibits release of LH and FSH

Describe the changes that take place in the uterus during the menstrual cycle

Uterus lining thickens

Progesterone maintains lining

If fertilisation has not occured, lining breaks down and is shed

If egg is fertilised, lining not broken down

Describe the passage of sperm in the female human

Semen (contains sperm and fluid from seminal vescicles) is ejaculated into the vagina

Sperm swims through uterus to oviduct

Where does fertilisation take place?

Oviduct

What is the function of the acrosome in the head of a sperm cell?

Contains digestive enzymes that break through the egg membrane

Why does sperm cell require mitochondria?

Respiration

Provides energy for tail

What is the function of the sperm cell’s tail?

Allows sperm cell to move

Explain why avoiding sexual intercourse at certain times of the menstrual cycle may not be a reliable method of birth control

• Ovulation may vary within a woman

• Sperm can survive for a number of days

Give the different stages of development during human reproduction

Gametes

Zygote

Embryo

Foetus

Baby

Explain how an 8 cell embryo is formed

Sperm and egg made by meiosis

Fertilisation in oviduct

Zygote implants in uterus wall

Divides by mitosis

What is the role of the placenta

Provides embryo with oxygen and nutrients from the mother’s blood

Removes urea and CO2 from embryo

Releases progesterone in late pregnancy

Describe how a developing foetus is supplied with nutrients

Nutrients (glucose, oxygen, amino acids) from mother’s blood

Diffuse through placenta

Placenta has a large surface area and thin walls

Umbilical cord join foetus blood supply to placenta

How is the placenta adapted for efficient exchange of substances

Villi - large surface area

Good blood supply from capillaries - steep concentration gradient

Thin walls- short diffusion distance

What is the role of amniotic fluid?

Protects foetus from physical impact

Acts as shock absorber

Where does the amniotic sac develop?

Uterus

What is a genome

The entire DNA of an organism

What is a gene

Section of DNA which codes for a protein

Where are genes found

In chromosomes within the nucleus

What is the role of genes

Control the activities of the cell

Determine which proteins are made

What is an allele

Different form of the same gene which gives rise to different characteristics

Define homozygous

Having two copies of the same allele

Define heterozygous

Having two different copies of the same allele

Define genotype

The alleles an organism has

Define phenotype

The physical appearance of an individual

Define recessive

Allele only expressed if the dominant allele is not present

Define dominant

Allele expressed even if only one is present

Define monohybrid interitance

Single gene responsible for phenotype

Define polygenic inheritance

Many genes combine to give a phenotype

Most phenotypic features are a result of polygenic inheritance

What is a carrier?

Someone who has a gene for a disease but doesnt suffer from any symptoms

What is a pedigree diagram

Shows how a genetic condition is passed from generation to generation

Possible to work out which is the dominant allele

Can then work out genotype of each person or animal in the diagram

What are the genotypes for males and females?

Males XY

Females XX

How is sex inherited

X chromosome from mother

All eggs contain one X chromosome

X or Y chromosome from father

50% of sperm cells contain one X chromosome, 50% contain one Y chromosome

Define haploid (n)

Contains 1 set of chromosomes, eg 23 in humans

Gametes are haploid

Define diploid (2n)

Contains 2 sets of chromosomes eg 46 in humans

Define clone

Genetically identical cell or organism

Give examples of when mitosis occurs

Growth , repair

Cloning

Asexual reproduction

Main steps of mitosis

Prophase

Metaphase

Anaphase

Telophase

What is the product of one round of mitosis

2 genetically identical cells

Cells are diploid

Where does meiosis occur

Sex organs

Meiosis produces gametes

What is the product of one round of meiosis

4 genetically varied cells

Haploid

Compare the features of mitosis and meiosis

Number of cell divisions : 1 for mitosis, 2 for meiosis

Number of daughter cells formed: 2 for mitosis, 4 for meiosis

Number of chromosomes in cells formed: DIploid in mitosis, haploid in meiosis

Type of cells formed: Body cells in mitosis, Sex cells in meiosis

Genetic variation in cells formed: None in mitosis, Variation in meiosis

How is variation within a species bought about

Genetics eg hair colour

Environmental conditions (eg. reduced growth due to poor diet when young)

Or a combination of both

How does genetic variation occur

Random fertilisation of gametes

Mixing of alleles from both parents

Meiosis

What is a mutation?

A rare, random change in the genetic material that can be inherited

Define evolution

All organisms alive today, and many more which are now extinct, evolved from simple life forms which first developed more than 3.2 billion years ago

Define the mechanism of Natural Selection

Variation within a species due to mutation

Individuals better adapted more likely to survive and reproduce

Alleles passed onto offspring

Repeats over many generations

Selected for alleles to become more prominent in population

How may bacteria become resistant to antibiotics?

Some bacteria have mutations that make them more likely to survive

The bacteria reproduce and pass on these favourable alleles to future bacteria

Soon the whole population of bacteria is resistant to the antibiotic.