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3 - Reproduction & Inheritance

(a) Reproduction (Plants)

Sexual Reproduction VS Asexual Reproduction

Sexual reproduction is the fusion of male and female gametes during fertilisation to produce non – identical offspring that inherit characteristics from both parents

Advantages	Disadvantages
Increases variation	Takes time and energy to find mates
The species can adapt to new environments due to the variation - a survival advantage	Difficult for isolated members of the species
Any disease is less likely to affect the population (due to variation)

Asexual reproduction does not involve sex cells or fertilisation

Only one parent is required so there is no fusion of gametes and no mixing of genetic information

As a result, the offspring are genetically identical to the parent and to each other (clones)

Advantages	Disadvantages
The population can be increased rapidly with the right conditions	No genetic variation in a population
Can exploit suitable environments quickly	The population is vulnerable to changes in conditions and may only be suited for one habitat
More time and energy efficient	Any disease is likely to affect the whole population (as there is no genetic variation)
Reproduction is completed much faster than actual sexual reproduction

Fertilisation

A gamete is a sex cell (in animals: sperm and ovum; in plants pollen nucleus and ovum)

Gametes differ from normal cells as they contain half the number of chromosomes found in other body cells

This is because they only contain one copy of each chromosome, rather than the two copies found in other body cells

In human beings, a normal body cell contains 46 chromosomes but each gamete contains 23 chromosomes
When the male and female gametes fuse, they become a zygote (fertilised egg cell)
This contains the full 46 chromosomes, half of which came from the father and half from the mother
The zygote divides to form two new cells, which then continue to divide and after a few days form an embryo
Cell division continues and eventually many of the new cells produced become specialised to perform particular functions and form all the body tissues of the offspring

Reproduction in Flowering Plants

Flowers are the reproductive organ of the plant

They usually contain both male and female reproductive parts

Plants produce pollen which contains a nucleus inside that is the male gamete

Unlike the male gamete in humans (sperm), pollen is not capable of locomotion (moving from one place to another)

This means plants have to have mechanisms in place to transfer pollen to the female parts of another flower

This process is known as pollination and there are two main mechanisms by which it occurs: transferred by insects (or other animals like birds) or by wind

The structure of insect and wind-pollinated flowers are slightly different as each is adapted for its specific function

Sepal	Protects unopened flower
Petals	Brightly coloured in insect-pollinated flowers to attract insects
Stamens	The male part of the flower, consisting of filament and anther
Filament	Positions anther to release male sex cell (pollen grain)
Anther	Produces and releases the male sex cell (pollen grain)
Carpel	The female part of the flower, consisting of stigma, style and ovary (containing the ovule)
Stigma	Top of the female part of the flower which collects pollen grains
Style	Connects the stigma to the ovary
Ovary	Produces the female sex cell (ovum)
Ovule	Contains the female sex cells (found inside the ovary)
Nectary	Produces a sugary solution called nectar to attract insects

Germination

Germination is the start of growth in the seed

Three factors are required for successful germination:

Water – allows the seed to swell up and the enzymes in the embryo to start working so that growth can occur
Oxygen – so that energy can be released for germination
Warmth – germination improves as temperature rises (up to a maximum) as the reactions which take place are controlled by enzymes

As CO2 is not necessary for germination but also does not inhibit it, it makes no difference whether it is present or not

Investigating Germination

Set up 4 boiling tubes each containing 10 cress seeds on cotton wool
Set each test tube as shown in the diagram below
Leave tubes in a set environment for a period of time: A, B and C incubated at 20°C; D placed in a fridge at 4°C
Compare results and see which tube has the greatest number of germinated seeds

(a) Reproduction (Humans)

Male Reproductive System

Glands	Produces fluids called semen that provide sperm cells with nutrients
Sperm Duct	Sperm passes through the sperm duct to be mixed with fluids produced by the glands before being passed into the urethra for ejaculation
Urethra	A tube running down the centre of the pets that can carry out urine or semen, a ring of muscle in the urethra prevents the urine and semen from mixing
Testis	Contained in a bag of skin (scrotum) and produces sperm (male gamete) and testosterone (hormone)
Penis	Passes urine out of the body from the bladder and allows semen to pass into the vagina of a woman during sexual intercourse

Female Reproductive System

Oviduct	Connects the ovary to the uterus and is lined with ciliated cells to push the released ovum down it. • Fertilisation also occurs here.
Ovary	Contains ova (female gamete) which will mature and develop when hormones are released
Uterus	Muscular bag with a soft lining where the fertilised egg (zygote) will be implanted to develop into a foetus
Cervix	Ring of muscle at the lower end of the uterus to keep the developing foetus in place during pregnancy
Urethra	A tube that passes urine out of the body from the bladder
Vagina	A muscular tube that leads to the inside of the woman’s body, where the male’s penis will enter during sexual intercourse and sperm are deposited.