Grade 12 Life Sciences Cheat Sheet

• This is a cheat sheet for Grade 12 Life Sciences.

How to Use this Study Guide

• Headings are hyperlinks to YouTube videos that match the learning topic or exam questions for practice.
• Pro-Tips highlight exam success strategies and common mistakes to avoid.
• Dedicated pages answer questions correctly, point out what to expect in tests/exams, and include the trickiest questions.

Question Words in Life Science

• Analyse: Examine and interpret; you often need to analyse a diagram/graph and explain what you see, providing reasons from the image, using what you observe.
• Calculate: A numerical answer is needed; you should always show your working out and give a unit of measurement in your answer.
• Classify: Group things based on common characteristics; you may be asked to classify based on a diagram, using what you can see, sometimes you will need to know structural characteristics.
• Compare: Show either similarities or differences; often this will be a table answer, or when writing a comparison your answers must complement each other.
• Define: Give a clear meaning; a set definition that is usually word for word.
• Describe: State in words the main points of a structure/process/phenomenon; you must provide the How, Where, When and Why: often requires lots of detail and must be answered with the correct sequence.
• Determine: To answer by examining something; you should look at the diagram/graph provided and come to a conclusion while providing a reason for your answer.
• Differentiate: Use differences; you will need to explain or list the differences between structures/diseases/processes, similar to compare.
• Discuss: Consider all info and come to a conclusion; take the results and provide reasons for why they may have happened.
• Explain: Provide a reason; this answer will often have a "cause" and "effect" structure, it will contain the How and Why (often confused with "describe").
• Identify: Name the essential characteristics; select visible structures/processes from the diagram, it normally requires you to label something.
• Label: Identify on a diagram or drawing; you should provide names for processes, structures, regions or products.
• List: List items but with no further detail; often these questions require single-word answers, if it asks for 2 but you give 3, they will only mark the first 2.
• Mention: Refer to relevant points; requires no further explanation, just a statement.
• Name: Give the name (proper noun) of something; one word answers, and if they ask to name 2 things but you name 4 they can only mark the first 2.
• State: Write down information without further discussion; short answers are given, normally one sentence or a phrase and there is no further explanation needed.
• Suggest: Offer an explanation or solution; these often higher-order questions require thinking above what has been provided and to make links between ideas.
• Tabulate: Draw a table; the answers in the table must read left to right and must complement each other, in other words they must consist of the same concept.

DNA Replication

• Occurs during interphase in the nucleus.
• Creates identical copies of DNA for mitosis or meiosis, replacing, repairing, or reproducing genetic material.
• Allows hereditary information to be passed on.
• Maintains correct chromosome number.
• The double helix unwinds, and hydrogen bonds break to separate the DNA into two separate strands to act as a template.
• Free-floating DNA nucleotides from the nucleoplasm join to their complementary DNA base triplets of A-T and G-C.
• Hydrogen bonds reform, DNA rewinds, and rezips, forming two identical strands.

Transcription

• Occurs during protein synthesis in the nucleus.
• Transports code from DNA to ribosome to create proteins.
• How:
  • double helix unwinds.
  • DNA unzips/weak hydrogen bonds.
  • Breaks into two separate strands.
  • One strand acts as a template.
  • Free floating RNA nucleotides from nucleoplasm join to their complementary DNA and base triplets of A-U and G-C which produces messenger RNA (mRNA).
  • mRNA now has the coded message for protein synthesis, moves from nucleus to cytoplasm, and attaches to ribosome.

Translation

• Occurs during protein synthesis, in the ribosome in the cytoplasm.
• Translates the mRNA into a functional set of amino acids joined by peptide bonds, forming a protein.
• mRNA inserts itself into the ribosome.
• The ribosome reads 3 letters at a time called a codon.
• The codon matches with the anticodon found on the transfer RNA (tRNA).
• Each tRNA carries a specific amino acid.
• tRNA anticodon matches the complementary mRNA codon.
• tRNA brings the required amino acid to the ribosome.
• The tRNA delivers the amino acid, these amino acids form a peptide bond between each other to form the require protein.

Meiosis Terminology

• Chromatin network: Intertwined DNA strand only visible during interphase.
• Chromosome: Condensed piece of DNA; can be single-stranded or double stranded.
• Chromatid: Formed after DNA replication; have two per chromosome.
• Centromere: Joins two chromatids.
• Homologous pair: Two chromosomes carrying similar genes, one paternal and one maternal.
• Synapsis: When homologous pairs move towards each other.
• Bivalent: When homologous pairs are touching.
• Chiasmata: Point at which homologous pairs touch.
• Locus: Gene location.
• Centrioles: Organelles that grow spindle fibres.
• Spindle fibre: Thread that pulls chromatids/bivalent apart.
• Centrosome: Temporary organelle that houses centriole.
• Recombinant chromosome: When homologous chromosomes exchange genes and become different.
• Crossing over: Where homologous pairs exchange genes to increase variation.

Meiosis

• Gametogenesis in ovaries and testes.
• Its purpose is to create 2 non-identical haploid cells that contain single chromosomes from homologous pairs.
• Halves the chromosome number to maintain the correct number and introduce variation. Meiosis 1 contains:
• Double-stranded chromosomes
• Homologous pairs are crossing over
• Non-identical/recombinant chromosomes Meiosis 2 contains:
• Single stranded chromosomes that creates 4 non-identical cells
• No crossing over taking places
• No homologous pair present
• Single-stranded chromosomes that may be recombinant

Reproductive Strategies

• External Fertilisation: Takes place in water, mostly aquatic vertebrates. It involves a large number of gametes to avoid predation, and courtship rituals that bring gametes closer, but it is wasteful in the number of eggs and fertilisation is not certain.
• Internal Fertilisation: Occurs in terrestrial vertebrates and doesn't require water to transport sperm It is an more certain as it involves less gametes and provides a protective shell/yolk, but it includes finding a mate, fewer reproduction opportunities and longer gestation.
• Ovipary: Eggs develop outside, fertilised either externally or internally. Aquatic animals produce many eggs with less yolk, whereas land animals produce very few eggs with more yolk, protection and parental care, but aquatic animals have very little often very little parental care while the later is susceptible to predators.
• Ovovivipary: Eggs are fertilised externally, eggs are kept inside then hatch internally. It involves a large amount of yolk and has protection from predators and provides young fully developed but has no na
• Vivipary: Internal fertilization, eggs do not have a shell, it is born live. It has a reduced egg number, nourishment and protection but there is no na

Amniotic Egg

• Structures and functions:
  • Shell provides protection/ prevents dehydration.
  • Yolk sac is the nutrition for embryo.
  • Albumin.
  • Allantois is reservoir for nitrogenous wastes.
  • Embryo.
  • Amniotic fluid and prevents dehydration and provides mechanical injury.
  • Amnion.
  • Chorion allows gaseous exchange, forms placenta in mammals.

Male Reproductive System

• Structures:
• Testes: Produces sperm cells and secretes testosterone
• Epididymis: Site of sperm maturation and storage.
• Seminferous Tubule: Site of sperm cell production.
• Vas Deferens: Transports sperm
• Prostate Gland: Produces secretions that contribute to semen and provides nutrients to sperm
• Seminal Vesicle: Produces secretion that contributes to semen and neutralises acid pH of vagina
• Cowpers Gland: Secretes fluid used in semen that assists with movement of the sperm cells.
• Penis: Organ used to deliver sperm to vagina
• Urethra: Tube that semen passes through during Ejaculation.
• Sperm Structure: Made up of the tail for locomotion, the neck consists of mitochondria to assist in cell respiration and the head region has the acrosome (digestive enzymes) and the nucleus.

Female Reproductive System

• Structures:
• Vagina: Passage which receives semen and penis and its the birth canal
• Uterus: The muscular organ its the location of pregnancy
• Cervix: Opening of uterus: protect uterus
• Endometrium: lining of uterus where embryo attaches and falls away every 28 days
• Myometrium: muscular layer of the uterus
• Fallopian Tube: Site of fertilization and its lined with cilia to move ovum along
• Ovary: Site of oogenesis and it secretes the hormones oestrogen and progesterone.

Menstrual cycle

• Oestrogen drops which results in FSH drops and the pituitary gland, after secretion, stimulates follicle.
• Follicle produces oestrogen which causes endometrium to thicken (repair) and matures follicle.
• Ovulation occurs which occurs where the corpus luteum drops.

Fertilisation to Implantation

• Stages:
• Fertilisation
• Zygote
• Morula
• Blastocyst
• Implantation
• Embryonic layers:
• Chorion: Is the outermostmembrane, and develops outgrowths that penetrates the endometrium and it Increases attachment surface area and contains capillary nework so that mother's blood and embryos blood never mix
• Placenta: Temporary organ, that secretes progestrone and ostrogen in order to maintain pregnancy and it allows a diffusion of oxygen and nutrients and removes foetal waste

Homologous and Heterozygous Crosses

• Monohybrid: working with only one set of alleles.
• Dihybrid: working with two sets of alleles.

Sex-Linked Disorders

• Working with disorders found on the x chromosome.
• The genotype of females XX allows them to carry the disorder but feel no symptoms. Males XY only have one X so if its affected they will experience symptoms.
• Haemonphilia: an unaffected male has a child with a woman that is a carrier for haemonphilia.
• Recessive and sex linked.
• Key:XH dominant, not haemophiliac, Xh, recessive, haemophiliac.

Genetic Modification

• Molecular Cloning involves a bacterial cell containing a plasmid and plasmid removed and a restriction enzyme removes a section of DNA then a Recombinant plasmid.
• Reproductive cloning involves eggs cells, somatic cells then nuclues insertion and removal.

Nervous System Structures

• Region and Structures :
• Meninges - Pia mater-outer, Arachnoid-middle, Dura mater -outer
• Cerebrum - corpus callosum ventricle, gyri and sulci
• Cerellum
• Brainstem medulla oblongata
• Spinal cord Function of each structure:
• Menings: protection
• Cerebrum: connection between hemispheres, filled with cerebral spinal fluid, increases surface area
• Cerebellum: coordinates voluntary movement, muscle tone, posture and balance
• Brainstem: pathway to and from brain, breathing, heartbeat, less important reflexes like sneezing or coughing
• Spinal cord: the pathway for impulses, integrative reflexes, primitive reflexes

Reflex Arc

• Pathway:
  • Stimulus => Sensory Neuron=> Dorsal Root => Grey Matter => Interneuron => Ventral Root => Motor Neuron => Effector

The Eye

• Structures and Functions:
• Conjunctiva: Protects and it is a clear membrane
• Ciliary body: Contains ciliary muscles and responsible for changing shape of lens
• Suspensory ligaments: Attached to lens and controls thickness of lens
• Pupil: It is the hole that allows light to enter eye and changes size
• Cornea: Is transparent, causes converging of refraction/ bending of light and it contsins pain receptors
• Iris: It contracts and relaxes to form pupil and responsible for how much light enters eye also contains radial and circular muscles
• Lens: Flexible structure, transparent and it refracts and bends light also it focuses light onto retina
• Sclera: It protects and maintains shape of eye
• Retina: It contains rods and cone and converts light into impulse
• Fovea: Highest point of visual acuity.
• Blind spot: Where there are no rods or cones and the area where optic nerve leaves eye.

Hearing

• Pinna traps sound waves into the ear canal which then causes the tympanic membrane to vibrate.
• The vibration is transmitted to the ossicles, which the ossicles amplify the vibration, and transmit it to the oval window.
• The oval window vibrates, creating waves in the endolymph/fluid of the cochlea.
• This stimulates the organ of Corti to convert the wave into an impulse.
• The impulse travels along the auditory nerve to the cerebrum, where it is interpreted as sound.

Endocrine System Structures

• Located in the brain.
• Hypothalamus secretes ADH and responds and releases ADH.
• Attached to hypothalamus.
• Butterfly-shaped gland on the trachea, below the larynx.
• Attached to the small Intestine.
• Pyramind-shaped gland.

Homeostasis

• Template answer for all endocrine/homeostasis processes: stimulus, receptor, Control centre, Corrective measure, Effectors, Response to stimulus, Result and Return to norm

What Is Natural Selection?

• Change in environmental conditions which alters micro and macro populations and Selects the most favourable characteristic in order to improve chances of survival
  • Large number of offspring, with large amounts of variation
  • Some have the characteristics, others do not
  • Environmental change leads to competition for resources
  • Some are suited, and ones that are unfavorable characteristics die
  • Organisms reproduce, and possess for the alleles for the characteristics for their offspring.

Evolution

• Speciation: populations are separated by geographic barriers, which cause natural selection, changes in alleles, lack of gene flow, and newly adapted species forms.
• Today: when animals are exposed to environments influenced by humans leads to new species to arise in order to survive new environments, due to antibiotic resistance.

Hominid Evolution.

• Features: brow ridge, sagittal crest, slope of face, teeth, prognathous jaw.
• Trends across species: smaller cranium, higher Sagittal Crest, increased slope of face and larger brow ridge and prognathous jaw
• The Turkana boy and 1st to use fire and is from the Homo ergaster family as well as canis.

Scientific Method

• Example investigation: Lizards of a certain species on an island are usually brown in colour so a scientists investigated the relationship between the colour of lizards in a population and their survival rate on an island.
• Scientific investigations will focus on: where to find it.
• Now to write it
• Why is it purpose
• the experiment will have aims, hypothesis, variables, controlled constant and variable
• Then after that there the experiment would be conducted so a reliability can be calculated
• after the experiment is conducted and valudity can be calculated then a conslucsion is ready to be done.