LEARNING OBJECTIVES
What you will be able to do
- compare asexual and sexual reproduction
- explain flower reproduction and germination
- describe human reproductive systems
- explain pregnancy and menstrual hormones
- describe STI control
AT A GLANCE
INTRODUCTION · THE BIG IDEA
How organisms produce offspring through asexual or sexual life cycles.
Reproduction preserves a species while producing either genetically identical or genetically varied offspring. The advantages of each strategy depend on the environment and purpose.
Plant and human reproduction share the same essential sequence: gamete production, transfer, nuclear fusion and development of a new organism.
SECTION 01
Asexual and sexual reproduction
Asexual reproduction uses one parent and produces genetically identical offspring. Sexual reproduction fuses haploid gamete nuclei to form a diploid zygote, creating genetically different offspring.
DETAILED EXPLANATION
- Sexual reproduction creates variation that can aid adaptation, but takes more time and energy.
- Crop growers use asexual methods for uniformity and sexual crosses for new combinations.
SECTION 02
Flowering plants
Stamens contain filament and anther; the carpel contains stigma, style, ovary and ovules. Sepals protect and petals often attract pollinators.
DETAILED EXPLANATION
- Insect flowers have conspicuous petals, nectar and sticky pollen; wind flowers have exposed anthers, feathery stigmas and abundant light pollen.
- A pollen tube grows through the style; a pollen nucleus enters an ovule and fuses with its nucleus.
- Seeds need water, oxygen and suitable temperature to germinate.
- A germination investigation uses equal seed batches and changes one condition at a time. Include a suitable control, keep other conditions constant and record how many seeds germinate.
SECTION 03
Human reproduction and development
Testes make sperm and testosterone; fertilisation usually occurs in an oviduct and implantation occurs in the lining of the uterus.
DETAILED EXPLANATION
- Ovaries produce eggs and hormones. Oviducts carry an egg towards the uterus; the cervix is the muscular opening of the uterus and the vagina receives the penis and acts as the birth canal.
- Sperm have a flagellum, mitochondria and acrosome enzymes. Eggs are large with energy stores and a jelly coat that changes after fertilisation.
- The zygote divides repeatedly to form an embryo, which implants in the uterus lining.
- Placenta exchanges nutrients, gases and wastes without normally mixing maternal and fetal blood.
- The umbilical cord connects the fetus to the placenta; amniotic fluid cushions it. Some pathogens and toxins can cross the placenta.
SECTION 04
Hormones, cycle and STIs
FSH stimulates follicle development and oestrogen secretion. Oestrogen rebuilds the uterine lining and promotes LH release; LH triggers ovulation. Progesterone maintains the lining and inhibits FSH and LH.
DETAILED EXPLANATION
- If no pregnancy occurs, progesterone falls and menstruation begins. In pregnancy, progesterone and oestrogen remain high.
- Testosterone and oestrogen regulate secondary sexual characteristics.
- HIV spreads through sexual contact, infected blood, shared needles and mother-to-child transmission; it may lead to AIDS.
- Barrier protection, testing, sterile needles and screened blood reduce STI spread.
STEP-BY-STEP EXAM EXAMPLE
Comparing sexual and asexual crop production
- Asexual propagation produces genetically identical plants quickly.
- Uniform crops preserve useful characteristics but share vulnerability to the same disease.
- Sexual reproduction combines genetic information from two gametes.
- Variation gives breeders new combinations to select.
Answer: Use asexual methods for uniformity and sexual reproduction to generate variation.
QUICK CHAPTER SUMMARY
The ideas to carry forward
- Asexual offspring are clones.
- Sexual reproduction creates variation.
- Pollination precedes plant fertilisation.
- Placenta supports exchange.
- Four hormones coordinate the cycle.
- STI control prevents pathogen transfer.
QUICK REVISION CHECKLIST
Can you do each of these without your notes?
- compare asexual and sexual reproduction
- explain flower reproduction and germination
- describe human reproductive systems
- explain pregnancy and menstrual hormones
- describe STI control