How many sets of chromosomes a gamete and zygote have and what they are called.

A gamete's nucleus is haploid, meaning it contains only one set of chromosomes.

A zygote has a diploid nucleus that contains two complete sets of chromosomes.

Discuss the advantages and disadvantages of sexual reproduction and asexual reproduction.

Asexual reproduction offers rapid population growth and requires only one parent, but lacks genetic diversity, making it advantageous in stable environments but vulnerable to changing conditions; sexual reproduction, while requiring two parents and a longer process, introduces genetic variation, enhancing adaptability to changing environments.

Application to Crop Production:

• Asexual reproduction:
  • Advantages: Useful for quickly propagating desirable crop varieties with consistent characteristics.
  • Disadvantages: Can lead to susceptibility to pests and diseases if the entire crop lacks genetic diversity.
• Sexual reproduction:
  • Advantages: Introduces genetic diversity into crops, which can enhance resistance to pests and diseases, and improve adaptability to changing environmental conditions.
  • Disadvantages: May require longer time to produce new crops compared to asexual reproduction.

Identify in diagrams and images and draw the following parts of an insect-pollinated flower:

sepals, petals, stamens, filaments, anthers, carpels, style, stigma, ovary and ovules

2 State the functions of the structures listed.

Sepals : Protect the flower bud before it opens.

Petals : Attract insects for pollination using their color, scent, and sometimes nectar guides.

Stamens: Produce the male gametes (pollen grains).

Filaments : Supports the anther and positions it to aid in pollen transfer.

Anthers : Produces and releases pollen grains, which contain the male gametes.

Carpels : Contains the female gametes (ovules) and is the site of fertilisation.

Stigma : The sticky tip of the carpel. Captures and holds pollen grains during pollination.

Style : Provides a pathway for the pollen tube to grow down to the ovary.

Ovary : Protects the ovules and develops into a fruit after fertilisation.

Ovules : Structures found inside the ovary. Contain the female gametes and develop into seeds after fertilisation.

Difference between insect and wind pollinated flowers.

Define pollination in plants and fertilisation

The transfer of pollen grains from an anther to a stigma.

When a pollen nucleus fuses with a nucleus in an ovule.

Define self-pollination and cross-pollination

Self : The transfer of pollen grains from the anther of a flower to the stigma of the same flower or a different flower on the same plant.

Cross : The transfer of pollen grains from the anther of a flower to the stigma of a flower on a different plant of the same species.

Discuss the potential effects of self-pollination and cross-pollination on a population, in terms of variation, capacity to respond to changes in the environment and reliance on pollinators.

Self-pollination results in low genetic variation, reducing a population's ability to adapt to environmental changes, but it decreases reliance on pollinators.

In contrast, cross-pollination leads to high genetic variation, increasing adaptability and resilience to new conditions, though it creates a greater dependence on pollinator populations.

Investigate and describe the environmental conditions that affect germination of seeds, limited to the requirement for: water, oxygen and a suitable temperature.

For seeds to germinate, they require sufficient water, which activates enzymes and softens the seed coat, allowing the embryo to grow;

sufficient oxygen for cellular respiration to provide energy for growth;

and a suitable temperature to ensure enzymes function correctly.

How pollen gets to the ovule and fertilises.

1. Pollination Occurs

A pollen grain lands on the stigma of a flower (either by wind, insect, etc.).

2. Pollen Tube Formation

The pollen grain germinates on the stigma and grows a pollen tube down through the style secreting enzymes to produce a pathway.

3. Pollen Tube Navigation

The tube grows towards the ovary and eventually reaches the ovule inside the ovary.

4. Entry into Ovule

The pollen tube enters the ovule through a small opening called the micropyle.

5. Nucleus Fusion (Fertilisation)

The male nucleus from the pollen grain travels down the pollen tube. It fuses with the female nucleus (egg cell) inside the ovule.

Define fertilisation in humans

The fusion of the nuclei from a male gamete (sperm) and a female gamete (egg cell).

Identify on diagrams and state the functions of the following parts of the male reproductive system:

testes, scrotum, sperm ducts, prostate gland, urethra and penis

Testes : Produce sperm (male gametes) and the male sex hormone, testosterone.

Scrotum : A sac of skin that protects the testes and maintains a temperature slightly lower than body temperature, which is essential for sperm production.

Sperm Ducts : Carry mature sperm from the testes to the urethra for ejaculation.

Prostate Gland : Produces a fluid that nourishes sperm and adds to the volume of semen.

Urethra : A tube that carries urine from the bladder and semen from the reproductive system out of the body.

Penis : The external male organ used for both urination and sexual intercourse, which delivers sperm into the female reproductive tract.

Identify on diagrams and state the functions of the following parts of the female reproductive system:

ovaries, oviducts, uterus, cervix and vagina

Ovaries : Produce and store ova (eggs) and female sex hormones like estrogen and progesterone.

Oviducts (Fallopian Tubes) : These tubes connect each ovary to the uterus. They provide the site for fertilisation to occur and transport the egg to the uterus using cilia and muscular contractions.

Uterus : muscular organ where the fertilised egg implants and develops into a fetus. It provides nourishment and protection for the growing fetus.

Cervix : The narrow, lower part of the uterus that connects it to the vagina. It produces mucus that helps to block bacteria from entering the uterus and opens to allow menstrual blood to flow out or a baby to pass through during birth.

Vagina : A muscular, elastic tube connecting the cervix to the outside of the body. It receives sperm during sexual intercourse and serves as the birth canal during childbirth.

Explain the adaptive features of sperm

A flagellum (tail) for swimming towards the egg,

Numerous mitochondria in the midpiece to provide the necessary energy for this movement.

Enzymes within the acrosome at the head of the sperm to digest the outer layers of the egg, allowing the genetic material to penetrate and fertilize it.

Explain the adaptive features of egg cells

A supply of energy stores in the cytoplasm to fuel the initial development of the embryo after fertilisation.

A jelly coat that changes to a hard, impenetrable barrier after fertilisation, preventing multiple sperm from entering the egg and ensuring proper development of the single zygote.

Compare male and female gametes in terms of:

size, structure, motility and numbers

The male gamete (sperm) is small, motile (the ability to move spontaneously and independently), and produced in huge number.

While the female gamete (egg/ovum) is large, non-motile, and produced in very small numbers.

• Male Gamete (Sperm):Has a distinct head (containing genetic material), a midpiece (for energy), and a tail (flagellum) for movement.
• Female Gamete (Egg/Ovum):Is a large, spherical cell containing the genetic material and abundant cytoplasm, along with stored nutrients.

Identify on diagrams and state the functions of the following in the development of the fetus:

umbilical cord, placenta, amniotic sac and amniotic fluid

• Placenta:
  • exchanges dissolved nutrients, gases and excretory products between the blood of the mother and the blood of the fetus.
  • Transfers antibodies to the fetus, giving it passive immunity.
  • Secretes hormones, such as progesterone and oestrogen, to maintain the pregnancy.
• Umbilical Cord:
  • Transports oxygenated blood, nutrients, and antibodies from the placenta to the fetus via an umbilical vein.
  • Carries deoxygenated blood and waste products from the fetus to the placenta via umbilical arteries.
• Amniotic Sac:
  • A protective, thin-walled membrane that surrounds the fetus.
• Amniotic Fluid:
  • Cushions the fetus from external bumps and mechanical shocks.
  • Helps to regulate the fetus's body temperature.
  • Provides space for the fetus to move, which aids in muscle and bone development.

*some pathogens and toxins can pass across the placenta and affect the fetus

Describe the roles of testosterone and oestrogen in the development and regulation of secondary sexual characteristics during puberty

Primary sexual characteristics are the reproductive organs, like testes and ovaries, present at birth and essential for reproduction. Secondary sexual characteristics are physical traits that develop during puberty under hormonal influence but are not directly involved in reproduction.

Role of Testosterone in Males

• Growth and voice:Testosterone causes growth spurts and the growth of the Adam's apple, leading to a deepening of the voice.
• Hair growth:It stimulates the growth of facial hair (beard and mustache), body hair, and pubic hair.
• Muscle and bone:Testosterone contributes to increased muscle mass and bone growth.
• Reproductive system:It is crucial for the maturation of the testes and the production of sperm, the male sex cells.

Role of Oestrogen in Females

• Breasts:Oestrogen triggers the development of breasts, the initial signs of puberty in girls.
• Hips:It promotes the widening of the hips.
• Reproductive system:Oestrogen is responsible for the development of female reproductive organs.
• Menstrual cycle:It initiates the menstrual cycle, which includes the maturation of eggs in the ovaries and their release during ovulation.
• Uterine lining:Oestrogen also plays a role in the growth and maintenance of the uterine lining.

Describe the sites of production of oestrogen and progesterone

• Oestrogen:Primarily produced by the developing ovarian follicles, and later by the corpus luteum.
• Progesterone:Produced by the corpus luteum, which forms from the follicle after ovulation.

Steps of menstruation cycle

1. Cycle starts: FSH causes follicle with egg to develop in ovary.
2. Developing follicle creates oestrogen which causes creation of uterus lining.
3. Once follicle is fully developed a surge in LH causes ovulation, now oestrogen starts to fall.
4. Follicle from which egg is released develops into a structure called a corpus luteum which secretes progesterone which keeps uterus soft and spongy. This causes FSH and LH to decrease.
5. If unfertilised the corpus luteum breaks down and progesterone drops menstruation occurs.
6. Then FSH and LH increase and cycle repeats.

If fertilised corpus luteum remains and uterus stays, and placenta develops. Placenta takes over secreting progesterone. High progesterone levels stops production of FSH so no more follicles develop in the ovaries.

Define a sexually transmitted infection (STI)

An infection that is transmitted through sexual contact.

How AIDS works

State that human immunodeficiency virus (HIV) is a pathogen that causes an STI.

HIV infection may lead to AIDS.

Ways HIV is transmitted

HIV is transmitted when infected body fluids from one person enter another person's bloodstream.

• Unprotected sexual intercourse (vaginal, oral, or anal)
• Sharing needles or syringes
• From mother to baby during pregnancy, childbirth, or breastfeeding
• Through infected blood transfusions

Explain how the spread of STIs is controlled

1. Use of Condoms

2. Screening and Testing : Regular STI testing helps detect infections early, especially in sexually active individuals. Early diagnosis allows prompt treatment and reduces further transmission.

3. Treatment of Infected Individuals : Use of antibiotics (for bacterial STIs) or antiviral drugs (for viral STIs like HIV) reduces the risk of spreading infection. Treating both partners prevents reinfection.

4. Education and Awareness.

5. Contact Tracing : Identifying and informing recent sexual partners of infected individuals helps stop the spread and ensures those partners also get tested and treated.

6. Avoiding Risky Behaviours : Limiting the number of sexual partners. Avoiding sex with people who have visible symptoms. Not sharing needles or syringes

7. Prevention of Mother-to-Child Transmission

• Pregnant women with STIs like HIV can receive antiretroviral treatment to reduce the chance of passing it to the baby.

State what chromosomes are

Chromosomes are made of DNA, which contains genetic information in the form of genes.

Define a gene

A length of DNA that codes for a protein.

Define an allele

An alternative form of a gene

how protein is made and types of proteins

• The sequence of bases in a gene determines the sequence of amino acids that make a specific protein.
• Different sequences of amino acids give different shapes and functions to protein molecules.
• These proteins include: enzymes that catalyze essential biochemical reactions, membrane carriers that transport substances across cell membranes, and receptors on the cell surface that bind to signaling molecules like neurotransmitters, allowing the cell to respond to its environment.

1. The gene coding for the protein remains in the nucleus, messenger RNA (mRNA) is a copy of this gene. mRNA molecules are made in the nucleus and move to the cytoplasm.
2. The mRNA passes into the ribosome.
3. The ribosome assembles amino acids into protein molecules. The specific sequence of amino acids is determined by the sequence of bases in the mRNA.

* most body cells in an organism contain the same genes, but many genes in a particular cell are not expressed because the cell only makes the specific proteins it needs.

How gender determination works.

There are 23 pairs of chromosomes in the nucleus of all diploid human cells. One of these pairs determines gender. These chromosomes are therefore called the sex chromosomes. Get one X from woman and Y or X from male. XX is girl. XY is boy.

haploid nucleus vs diploid

I haploid nucleus is a nucleus containing a single set of chromosomes.

A diploid nucleus is a nucleus containing two sets of chromosomes.

Describe mitosis vs meiosis

Mitosis : nuclear division giving rise to genetically identical cells. Exact replication of chromosomes occurs before mitosis. During mitosis, the copies of chromosomes separate, so each daughter cell gets one complete set of chromosones. Stem cells as unspecialised cells that divide by mitosis to produce daughter cells that can become specialised for specific functions.

Meiosis : a reduction division in which the chromosome number is halved from diploid to haploid resulting in genetically different cells. makes a gamete.

Define inheritance

The transmission of genetic information from generation to generation.

Define genotype

The genetic make-up of an organism and in terms of the alleles present.

Define phenotype

The observable features of an organism.

Define homozygous

Having two identical alleles of a particular gene.

Define heterozygous

having two different alleles of a particular gene

homozygous vs heterozygous breeding

Two identical homozygous individuals that breed together will be pure-breeding.

A heterozygous individual will not be pure-breeding.

Define a dominant allele

An allele that is expressed if it is present in the genotype.

Define a recessive allele

An allele that is only expressed when there is no dominant allele of the gene present in the genotype.

Explain how to use a test cross to identify an unknown genotype

In a TEST CROSS,

1. the organism with the dominant trait is always crossed with an organism with the recessive trait.
2. if ANY offspring show the recessive trait, the unknown genotype is heterozygous.
3. if ALL the offspring have the dominant trait, the unknown genotype is homozygous dominant.

Define codominance

a situation in which both alleles in heterozygous organisms contribute to the phenotype

Describe a sex-linked characteristic

A feature where the gene responsible is located on a sex chromosome and that this makes the characteristic more common in one sex than the other.

For example colour blindness recessive gene is on X so its more common in men because they only have on X chromosome they have a 50% chance of getting it. while for women the chance is 1 in 4 and they will need both recessive together.

Explain the inheritance of ABO blood groups:

Alleles are I^A, I^B and I^o and the phenotypes are A, B, AB and O blood groups.

I^A and I^B are more dominant over I^o and A and B codominate.

So A is AA or AO

B is BB or BO

AB is AB

O is OO

Define variation

The differences between individuals of the same species.

Define continuous variation

a range of phenotypes between two extremes; examples include body length and body mass.

*discontinuous variation is usually caused by genes only and continuous variation is caused by both genes and the environment

Define discontinuous variation

a limited number of phenotypes with no intermediates; examples include ABO blood groups, seed shape in peas and seed colour in peas

*discontinuous variation is usually caused by genes only and continuous variation is caused by both genes and the environment

Describe gene mutation

A random change in the base sequence of DNA.

*Mutation is the way in which new alleles are formed. Ionising radiation and some chemicals increase the rate of mutation.

sources of genetic variation in populations

Mutation,

meiosis,

random mating

and random fertilisation.

Define an adaptive feature

An inherited feature that helps an organism to survive and reproduce in its environment.

Explain the adaptive features of hydrophytes and xerophytes to their environments

Hydrophytes are water plants with adaptations like:

• aerenchyma (air spaces)for buoyancy and gas exchange and aerenchymatous tissues provide buoyancy and support in the water.
• Reduced root systems Roots are often small or absent because water is readily available, making extensive root development unnecessary.
• broad, thin leaves to increase light absorption and buoyancy.
• Stomata on Upper Surface : Stomata are typically located on the leaf's upper side, exposed to air, to increase the efficiency of gas exchange.

In contrast, xerophytes are plants adapted to dry conditions with features such as:

• Thick, waxy cuticles to prevent water loss.
• Reduced leaf surface area (e.g., spines) to minimize transpiration.
• Deep or extensive root systems to access water.
• Succulent Tissues : Some xerophytes have specialised cells in their leaves and stems that store water, serving as a reservoir during drought period.
• Sunken Stomata: Stomata are sometimes located in pits or depressions on the leaf surface, creating a humid microenvironment that reduces water loss.
• CAM Photosynthesis : Some xerophytes perform Crassulacean Acid Metabolism (CAM), where stomata open at night to take in carbon dioxide, closing during the day to conserve water.

Describe natural selection

(a) genetic variation within populations

(b) production of many offspring

(c) struggle for survival, including competition for resources

(d) a greater chance of reproduction by individuals that are better adapted to the environment than others

(e) these individuals pass on their alleles to the next generation

*The development of strains of antibiotic resistant bacteria as an example of natural selection.

Define adaptation

The process, resulting from natural selection, by which populations become more suited to their environment over many generations.

Describe selective breeding

(a) selection by humans of individuals with desirable features

(b) crossing these individuals to produce the next generation

(c) selection of offspring showing the desirable features

Outline the differences between natural and artificial selection