Eye Anatomy and Light Reflex

• Response to changes in light intensity is a reflex action to protect the retina

Dark Environment

• Photoreceptors detect a decrease in light intensity
• Radial muscles of the iris contract, and circular muscles relax
• The pupil dilates and the diameter widens
• More light enters the eye

Light Environment

• Photoreceptors detect an increase in light intensity
• Radial muscles of the iris relax, and circular muscles contract
• The pupil constricts, and the diameter narrows
• Less light enters the eye

Eye Anatomy

• Eye: Sense organ with receptor cells sensitive to light and color
• Conjunctiva: Protects and lubricates the eye by producing mucus and tears
• Cornea: Transparent, refracts light as it enters the eye
• Sclera: Tough white outer layer, protects it from damage
• Pupil: Hole allowing light to enter the eye
• Iris: Controls the amount of light that enters the pupil
• Lens: Transparent disc that changes shape to focus light on the retina
• Ciliary muscle: Ring of muscle, contracts and relaxes to change lens shape
• Suspensory ligaments: Connects the ciliary muscle to the lens
• Retina: Has rods and cones, converts visual stimuli into impulses
• Fovea: Area with the highest concentration of cones on the retina
• Optic nerve: Sensory neuron that carries impulses between the eye and the brain
• Vitreous humour: Jelly-like substance that helps the eye maintain its shape

Thermoregulation

• Blood temperature receptors in the skin provide information to the hypothalamus

High Body Temperature

• Skin hairs lie flat, allowing air to circulate and heat to leave by radiation
• Sweat glands secrete sweat, cooling the body through evaporation
• Heat energy causes sweat to change state from liquid to gas, taking heat energy with it
• Vasodilation increases skin capillary diameter and blood flow
• Faster blood cools the body, more heat is lost through radiation

Low Body Temperature

• Skin hairs are pulled upwards, trapping air and acting as an insulator
• Skeletal muscles contract rapidly, causing shivers
• Energy from respiration is required, but some is released as heat
• Vasoconstriction decreases skin capillary diameter and blood flow
• Reduced blood flow through the skin surface slows, and less heat is lost through radiation

The Endocrine system

• Hormones are chemical substances produced by glands that travel in the blood to organs
• Hormones control the activity of target organs
• Hormones are destroyed by the liver after being used

Key Hormones

• Adrenaline (Source: adrenal): Increases heart and breathing rate and blood flow to muscles
• Insulin (Source: pancreas): Lowers blood glucose by causing uptake and conversion of glucose in blood into glycogen by muscles and liver
• Glucagon (Source: pancreas): Increases blood glucose by causing conversion of stored glycogen in liver into glucose, which is released into the blood
• ADH (Source: pituitary): Controls water content of blood by increasing permeability of collecting ducts, increasing reabsorption of water from urine
• Testosterone (Source: testes): Male sex hormone, develops secondary sex characteristics

Reproduction

• 3A. Reproduction

Haploid and Diploid Cells

• Haploid cells contain a single set of chromosomes (23 in humans)
• Diploid cells contain two copies of each chromosome (46 in humans)
• Humans have 23 different pairs of chromosomes
• Most human cells are diploid

Gametes and Zygotes

• Gametes are haploid sex cells (ovum / sperm / pollen nucleus)
• Zygote is a diploid fertilized egg cell that divides by mitosis
• Fertilization is the fusion of a male and female gamete

Reproduction Types

• Sexual reproduction involves forming a new organism by fusing two haploid gametes
• Asexual reproduction involves the offspring coming from a single organism

Sexual Reproduction vs Asexual Reproduction

Sexual Reproduction

• Involves 2 parents
• Requires 2 parents that cannot reproduce individually
• Gamete fusion occurs with male and female gametes fusing
• Cell division occurs through meiosis
• Offspring produced are non-identical
• Adaptability is high, with increased variation and higher survival chances
• Population growth is slow due to time and energy consumption

Asexual Reproduction

• Involves 1 parent
• Requires only 1 parent that can reproduce individually
• No gamete fusion
• Cell division occurs through mitosis
• Offspring produced are clones
• Adaptability is low, with no genetic variation, making them vulnerable to changes
• Population growth is quick, and time/energy efficient

Plant Reproduction

• Flower, plant reproductive organ

Flower Anatomy

• Sepal: Protects the unopened flower
• Petals: Brightly colored in insect-pollinated flowers to attract insects
• Nectary: Produces nectar to attract insects
• Stamen: Male part, consisting of filaments and anthers
• Filaments: Positions the anthers to release pollen grains
• Anthers: Produces and releases pollen grains
• Carpel: Female part, consisting of stigma, style and ovary
• Stigma: Collects pollen grains
• Style: Connects the stigma to the ovary
• Ovary: Contains the ovules
• Ovule: Produces the female sex cell (ovum / ova)

Pollination

• Transfer of pollen grain from the anther to the stigma of another flower
• Pollen grains have no locomotion and pollination is done by insects or wind

Seed Formation

• Occurs when pollen reaches the stigma of plants

Fertilization and Germination

• The nucleus in the grain slips down the tube and fuses with an ovum in an ovule
• The ovum is fertilized, the zygote is formed and it starts to divide
• Ovule becomes the seed and the ovule wall becomes the testa (seed coat) while the ovary becomes the fruit
• Germination is the growth of seeds
• Seed consists of an embryo, cotyledon (starch food store), and testa (seed coat)
• Water makes the seed swell, softens testa so it splits and activates enzymes in embryos
• Oxygen is needed to release energy for germination
• Warmth improves the speed of enzyme-catalysed germination
• The seed absorbs water, which makes it swell and the testa splits open
• Oxygen enters and water activates enzymes that begin the plant's growth
• Amylase breaks starch down into glucose for respiration to occur
• Shoot grows and roots develop, and leaves unfurl for photosynthesis

Pollination by Insects vs Wind

Insect Pollination

• Pollen: smaller amounts, larger and heavier, sticky/spiky
• Petals: large, brightly colored
• Scent and Nectar: present, to attract insects
• Success rate: higher chance of success, efficient
• Anthers: within flowers, stiff and firm to brush against insects

Wind Pollination

• Pollen: larger amounts, small and lightweight
• Petals: small and dull
• Scent and Nectar: not present
• Success rate: lower chance of success
• Anthers: outside flowers, swings on long filaments

Asexual reproduction

• One parent is needed for asexual reproduction, and the offspring is genetically identical (clones)

Runners

• Natural asexual reproduction, e.g. strawberries
• Plants grow horizontal runners that contain small plantlets, which grow roots and grow independently

Cuttings

• Artificial asexual reproduction
• Stem are dusted with rooting powder. Rooting powder contains auxin to encourage the growth of new roots

Tissue culture / micropropagation

• Artificial asexual reproduction
• Small pieces of plant are grown by using nutrient media

Human Reproduction

Male Reproductive System

• Glands: Provide sperm cells with nutrients (seminal vesicle, prostate gland)
• Testis: Produces sperm and testosterone, contained in the scrotum
• Sperm duct: The duct that sperm passes through to be mixed with semen from glands
• Urethra: Carries out urine and semen, a muscle ring prevents them from mixing
• Penis: Passes urine and semen out of the body
• Prostate: Secretes alkaline fluid and electrolytes

Fertilization and Development

• Fertilization is the fusion of the nuclei from a male gamete (sperm) and a female gamete (ovum) and occurs in the oviducts in human females
• Spongy tissue in the penis filled with blood becomes erect.
• At the climax, semen is ejaculated from the penis into the vagina

Foetus Development

• Development: 9 month gestation, zygote divides by mitosis to form embryo
• The amniotic sac breaks, uterus muscles contract, cervix dilates, baby is passed out the vagina, the umbilical cord is cut and afterbirth is delivered

Placenta

• Plays a role during gestation of the foetus
• Molecules move across by diffusion, not mixing
• It detaches from the uterus after birth and is pushed out during afterbirth.
• Provides substances like glucose, amino acids, fats, oxygen, water.
• Removes waste like carbon dioxide, urea.
• Acts as a barrier, prevents pathogens and toxins from entering

Amniotic Fluid

• Surrounds and cushions the foetus during development
• Cushions and protects the foetus from outside forces
• Acts as a lubricant, reducing friction againist the uterus walls

Menstrual Cycle

• Occurs in females after puberty and before menopause, controlled by hormones
• Ovaries mature and release one ovum every 28 days for fertilisation
• Uterus lining thickens to prepare for implantation and pregnancy

Hormones in the Menstrual Cycle

• FSH: pituitary gland, causes the follicle in the ovary to produce oestrogen
• Oestrogen: from ovaries, causes the wall to thicken
• LH: pituitary gland, stimulates corpus luteum to produce progesterone
• Progesterone: from ovaries, causes uterus lining to remain thick

Puberty

• Primary sexual characteristics are reproductive organs
• Secondary sexual characteristics are hormone release that cause changes during puberty

Genetics

• GENOME = the entire genetic material of an organism.
• DNA = a double helix formed of two strands linked by paired bases.
• GENE = short DNA section that codes for a specific protein, controls our characteristics.
• CHROMOSOME = long strands of DNA coiled with histone proteins in nuclei.

DNA and RNA components

• Base pairs = adenine, thymine, guanine, cytosine, uracil

DNA & RNA Definition

• DNA Deoxyribonucleic Acid = a double helix polymer containing genetic information
• RNA: Ribonucleic acid = single-stranded molecule responsible for protein synthesis

Protein synthesis

• Transcription = DNA is transcribed onto an mRNA (messenger RNA) molecule
• DNA helix is untwisted and unzipped in the nucleus. Enzyme DNA helicase does this
• mRNA attaches to a ribosome that reads its bases in codons
• A codon codes for a specific amino acid. tRNA has matching anticodons

Genetic Terms

• Heterozygous: when the two alleles of a gene are different
• Polygenic Inheritance: when phenotypes are controlled by more than one gene, height
• Monohybrid Inheritance: when phenotypes are controlled by a single gene

Genetic Diagrams

• Punnett square: Shows combinations of alleles in offspring
• Family pedigree: Traces pattern of inheritance of characteristics through generations

Mitosis and Meiosis

• Mitosis: Cell division, produces two genetically identical diploid daughter cells
• Meiosis: Cell division, produces four genetically different haploid daughter cells

Variation

• Variation difference in DNA sequences of individuals within the same species
• Gametes are genetically different due to meiosis

Genetic Variation

• Phenotypes are dependent on inherited alleles from parents
• Environmental Variation characteristics caused by difference in lifestyle / climate / diet

Mutation

• Rare, random, spontaneous changes in genes (DNA) that can be inherited
• Mutations alter base pair sequence in DNA, which can code for different proteins

Increasing Mutation

• Rare, random, spontaneous changes in genes (DNA) that can be inherited
• Mutations alter base pair sequence in DNA, which can code for different proteins

Increasing Mutation Rates

• Ionising radiation or chemical mutagens
• These damage bonds and cause changes in base sequences

Natural selection

• cumulative change in the genetic makeup of a population over many generations
• There is variation within species, caused by different genes from sexual reproduction and mutations

Antibiotic resistance

• Chemicals that kill or inhibit growth and reproduction of bacteria
• Is when bacteria become resistant to antibiotics