Natural Selection & Evolution

• Natural selection involves organisms with favorable genes and characteristics being "selected" or "favored" to survive and pass on their genes.
• Organisms with certain inherited traits are more likely to survive and reproduce compared to others.

Evolution

• It is the gradual change in the inheritable characteristics of a population over time
• The accumulation of genetic differences over long periods leads to new types of living organisms development

Process of Natural Selection

• Pre-existing Variation: Natural variation exists within a population (e.g., rabbits with dark, intermediate, and light-colored fur)
• Selection Pressure: Selective force selects the variation that best fits the environment (e.g., individuals with dark fur are less easily detected by predators)
• Differential Survival & Reproduction: Individuals with the selected variation survive and reproduce, passing on the favorable allele (e.g., dark-furred rabbits reproduce, passing on alleles for dark fur)
• Evolutionary Change: Over generations, the population changes, with more individuals possessing the selection variation (e.g., more dark-furred rabbits over time)

Key Features of Natural Selection

• Limited resources lead to competition for food, shelter, and mates.
• Organisms can produce more offspring than can survive to maturity.
• A struggle for existence results from overproduction and resource limits, creating competition.

Examples of Natural Selection

• Dark peppered moths camouflage better on soot-covered tree trunks.
• Antibiotic-resistant bacteria evolved due to antibiotic overuse, where genetic mutation allowed resistant bacteria to survive and reproduce, leading to antibiotic-resistant strains.

Artificial Selection

• This method is used to produce plants and animals with desirable traits
• Example: Belgium Blue cattle with muscular characteristics are bred. Offspring lacking muscular traits are eliminated. Those with muscular traits are kept for breeding.

Asexual Reproduction

• A process results in genetically identical offspring from one parent, without gamete fusion
• Mitosis is cell division for genetically identical cells with maintained chromosome number

Types of Asexual Reproduction

• Stem Tube: modified stem for propagation
• Rhizome: horizontal underground stem
• Runner: horizontal stem that roots at nodes

Advantages of Asexual Reproduction

• Only one parent is required
• Fusion of gametes is not require
• Beneficial qualities are always passed to offspring
• It is faster compared to sexual reproduction

Disadvantages of Asexual Reproduction

• No genetic variation in offspring, making the species poorly adapted to environmental changes and vulnerable to extinction from disease

Sexual Reproduction

• It involves the fusion of two gametes forming a zygote, producing dissimilar offsprings.
• Zygote: A single cell formed when male gamete fuses with female gamete

Meiosis

• Cell division yields genetically dissimilar cells with halved chromosome numbers
• Reduction division reduces chromosomes

Advantages of Sexual Reproduction

• Offspring may inherit beneficial qualities from both parents
• It provides genetic variation in offspring

Disadvantages of Sexual Reproduction

• Two parents are required
• Fusion of gametes is required
• It is slower than asexual reproduction

Comparing Asexual and Sexual Reproduction

• Asexual reproduction doesn't involve gamete fusion and requires only one parent, resulting in genetically identical offspring faster
• Sexual reproduction involves fusion of male & female gametes to form a zygote and requires two parents, resulting in genetically dissimilar offspring slower

Reproduction in Plants

Flower Structure

• Petals: brightly colored to attract insects for pollination

Sepal

• Sepal: Encloses and protects flower parts in the bud stage

Flower Stalk

• Connects flower to stem

Stamen

• Filament: Holds anther for pollen dispersion
• Anther: Produces pollen grains, releasing them when mature
• Pollen Grains: Contain male gametes, produced by meiosis

Carpel (Pistil)

• Stigma: Receives pollen, secreting fluid to stimulate germination
• Style: Holds stigma in position for pollen trapping
• Ovary: Contains one or more ovules, each with a female gamete (ovum) produced by meiosis

Pollination Types

Transfer of pollen grains from anther to stigma with two types:

• Self-pollination
• Cross-pollination

Self-Pollination

• Transfer of pollen from anther to stigma on the same flower or plant.
• It occurs in bisexual flowers with synchronized maturation of anthers and stigmas

Advantages of Self-Pollination

• Only one parent is needed
• Beneficial qualities are more likely to be passed to offspring
• There is no need to depend on external factors for pollination
• A higher probability of pollination
• Less expenditure of energy and pollen

Disadvantages of Self-Pollination

• Less genetic variation implies being less adapted to changing environments
• It may lead to offspring becoming weaker, smaller, and less resistant to diseases

Cross-Pollination

• Transfer of pollen grains from one plant to the stigma of another plant of the same species.
• It occurs in bisexual plants with different maturation times or distant anthers and stigmas

Advantages of Cross-Pollination

• Beneficial qualities inherited from both parents
• Greater genetic variation increases the chances of survival
• More viable seeds are produced, implying the seeds survive longer before germination

Disadvantages of Cross-Pollination

• The requirement of two plants
• It depends on external factors for pollination
• A lower probability of pollination
• More energy and pollen wasted

Insect-Pollinated Flowers

• Have Large brightly coloured Petals
• They have a present Nectar
• Exhibiting fragrant or sweet-smelling Scents
• Small, compact stigmas

Wind-Pollinated Flowers

• It small dull-coloured petals
• they do not have a Nectar
• Exhibiting Odourless/scentless
• Large, feathery stigmas.

Example of Insect-Pollinated Flower

• Clitoria (Blue Pea Flower):
• Petals: Brightly colored, nectar guides present
• Stamens: Nectar found at the bottom with insects that must brush past the stamen
• Stigma: Small and compact
• Style: Long, curved, hairy process of pollination

Wind-Pollination in Grasses

• Characteristics: small, grouped inflorescences, dull-colored, scentless, and no nectar/flowers enclosed and protected by bracts/scales

Features

• Has feathery stigmas for trapping airborne pollen and stamens with external anthers for wind dispersal.

Seed Development after Fertilization

• Ovary develops into fruit and ovule into seed.
• The zygote becomes the embryo
• Petals, style, and anthers fall, but stigma remains on the fruit

Seed Structures

• Cotyledons: Procure food for seed for germination

Male Reproductive System Functions

• Production, storage, and transport of sperm & semen
• Discharge of sperm within the female reproductive tract
• Production and secretion of male sex hormones

Penis

• Erectile function, delivering sperm to the vagina
• Testes produce testosterone and sperm
• Scrotum maintain sperm-forming cells at cooler temperatures

Sperm Transportation

• Sperm duct (vas deferens) delivers sperm to the urethra during ejaculation
• Urethra conveys both sperm and urine, with urine flow blocked during erection
• Semen contains streamlined sperm cells

Sperm Glands

• Prostate Gland releases of fluid that nourishes sperm while providing protection from the natural acidity of the vagina

Female Reproductive System Functions

• Production of egg cells (ova)
• Transport of ova to fertilization site (oviduct/fallopian tubes)
• Provision of safe environment for foetus development (uterus)
• Production of female sex hormones for reproductive cycle maintenance

Ovaries

• Ovaries are the sites of gamete production

Ovarian Follicles

• Each comprise of a single developing egg cell (ovum), are surrounded by nourishing & protective cells
• Follicles also produce oestrogen and progesterone (by corpus luteum)

Fallopian Tubes

• Site of fertilization
• Released eggs travel to the uterus with Sperm is present, fertilization occurs in the upper oviduct and the other way round

Uterus

• Actual site of pregnancy where the embryo grows
• Cervix opens into the vagina, facilitating flow to and directs sperm into uterus
• Vagina serves as a repository for sperm cells

Male Gametes

• Head, middle piece, and tail
• Nucleus contains X or Y chromosomes
• 60 μm long, with 2.5 μm head
• Has a tail and swim motion
• The numbers are large sperm released

Female gametes

• Spherical in shape
• One X chromosome
• diameter of 120 to 150 um
• Passive movement caused by cilia
• one egg is released

Menstruation

• It is a process where blood from the uterus is discharged through the vagina every month which is caused by breakdown of endometrium

Menstrual Cycle

• A monthly cycle of events including menstruation and ovulation
• Stages in menstrual cycle:
• Menstruation: Uterine lining and unfertilized egg shed with some blood
• Post-Menstruation: Ovary produces oestrogen, repairing and thickening the uterine lining
• High oestrogen leads to ovulation
• Ovulation: Release of a mature egg(s) from the ovary into the oviduct around day 14, with two ovaries alternating
• The egg survives 24 hours and sperm lasts 5 days
• Post-Ovulation: Ovary produces progesterone to prevent additional eggs
• Uterine: lining thickens for implantation and there is a decrease in oestrogen production
• the process start again if fertilization does occur

Hormones Affecting Menstrual Cycle

• FSH (Follicle-Stimulating Hormone): Stimulates growth and maturation of ovarian follicles and sperm
• LH (Luteinizing Hormone): Causes ovulation and testosterone production
• Progesterone and oestrogen are produced by ovaries

Ovarian Cycle

• monthly preparation and shedding of the egg cells from the ovary Uterine cycle: buildup of lining of the uterus

• No fertilisation

• Egg breaks down

• low progesterone levels

• uterine lining breaks down

• Fertlisation occurs

• Egg becomes Zygote

• It develops into an embryo

• It embeds into to the lining of uterus

• Implantation

• Sweeps along the oviduct

• the embryo gets embedded in in uterine lining

• Placenta

• begins to grow from embryo into the uterine lining

• The umbilical cord attaches embryo to placenta

• Development of amniotic sac

• This occurs around the same time as the placenta

• The fetus continues to develop

Sexually Transmitted Infection

• disease spread/transmitted through sexual intercourse
• semen/vaginal fluid can be infected

Human Immunodeficiency Virus

• It destroys the body's immune system
• Can develop into AIDS
• Signs are:
• Brain infection
• Persistent fever
• Pneumonia
• Diarrhoea
• Cancer etc

Prevention

• Keep sexually safe
• Abstain form sex
• Use new sterile needles

Fertility

• Males causes are low sperm count or erectile dysfunction
• Females causes are:
• Lack of of eggs/failure to ovulate
• Blocked Fallopian tubes

Options

• Treating medical condition
• Assisted fertilization with eggs
• Surgically remove eggs
• Mix with sperm to start devloping
• Transfer into uterus