Why is DNA in the nucleus stored as a double strand?
- Stability & Protection: The double helix structure shields the genetic code from chemical damage, making DNA much more stable and durable than single-stranded RNA, which is why DNA serves as the long-term archive.
- Accurate Replication: When cells divide, the strands separate, and each acts as a template (complementary base pairing) to build a new partner strand, ensuring daughter cells get identical DNA.
- Error Checking & Repair: If one strand gets damaged or has a mistake, the other strand provides the correct sequence, allowing cellular machinery to repair the error, preventing mutations.
- Information Storage: The sequence of bases (A, T, C, G) on one strand dictates the sequence on the other, creating a robust system for encoding genetic instructions.
The cell can be divided into what three main compartments?
- Nucleus
- Cell membrane
- Cytoplasm
Summarise metabolism and energy production inside the cell
Cells create energy (ATP) via respiration or photosynthesis, fuelling all activities.
Summarise protein synthesis within the cell
Making proteins (enzymes, structures, signals) from DNA instructions (transcription to RNA, then translation to protein).
Summarise transcription
Transcription copies a gene’s DNA into messenger RNA (mRNA) in the nucleus
Summarise translation
Translation uses that mRNA code at ribosomes in the cytoplasm to build a chain of amino acids (a protein)
Describe key structure and components of the cell membrane
- Phospholipid Bilayer: The fundamental structure, where phospholipids arrange with their water-loving (hydrophilic) heads facing outward and water-fearing (hydrophobic) tails facing inward, creating a barrier.
- Proteins: Embedded within or attached to the bilayer, these perform crucial roles like transporting molecules, receiving signals (receptors), and cell recognition.
- Carbohydrates & Cholesterol: Often found on the outer surface, contributing to cell recognition and membrane stability (cholesterol in animal cells).
The glycocalyx
The glycocalyx is a sugar-rich, hair-like layer coating most cells, made of glycoproteins, glycolipids, and proteoglycans, acting as a crucial interface between the cell and its environment, controlling cell recognition, adhesion, fluid balance (especially in vessels), and signaling, with damage linked to diseases like sepsis, diabetes, and heart issues
What molecules move across the membrane via passive transport?
- Simple Diffusion: Small, uncharged molecules (O₂, CO₂) pass directly through the lipid bilayer down their concentration gradient.
- Facilitated Diffusion: Ions and larger polar molecules (like glucose) move through specific channel or carrier proteins down their gradient.
- Osmosis: The diffusion of water across a selectively permeable membrane from an area of high water potential (low solute) to low water potential (high solute).
What moves across the cell membrane via active transport?
- Primary Active Transport: Proteins (like the sodium-potassium pump) use ATP to directly pump substances against their gradient (e.g., 3 Na⁺ out, 2 K⁺ in).
- Secondary Active Transport (Co-transport): Uses the energy from an ion’s gradient (established by primary active transport) to move another substance (e.g., glucose co-transported with Na⁺)
What processes are involved in bulk transport across the membrane?
Endocytosis: Cell membrane engulfs substances, forming a vesicle (e.g., phagocytosis, pinocytosis).
Exocytosis: Vesicles fuse with the membrane to release contents outside the cell (e.g., hormone release).
How do we see?
- We see when light enters our eyes, gets focused by the cornea and lens onto the retina, which converts it into electrical signals sent via the optic nerve to the brain, and our brain interprets these signals as images, colors, and depth.
- It’s a fast process where the cornea and lens focus light onto the retina, specialized cells (rods for low light, cones for color) detect it, and the optic nerve transmits signals to the brain for processing into understandable visuals.
The eye’s roles in sight
- Light Enters: Light rays come into the eye through the clear cornea and pupil.
- Focusing: The cornea bends the light, and the lens fine-tunes the focus onto the retina.
- Light Control: The iris (colored part) adjusts the pupil’s size, letting in more or less light as needed.
- Image Capture: The retina, at the back of the eye, has millions of photoreceptors (rods and cones) that detect light and color.
- Signal Creation: Rods help see shapes and dim light, while cones see color; they convert light into electrical signals.
The brain’s role in sight
- Transmission: The optic nerve acts like a cable, carrying these electrical signals from the retina to the brain.
- Interpretation: The brain flips the upside-down image from the retina right-side up and combines inputs from both eyes for depth perception.
- Recognition: It processes these signals into recognizable images, allowing you to see objects, colors, and movement.
How do we hear?
- We hear when sound waves enter the outer ear (pinna/auricle), which focuses the energy to vibrate the eardrum, and are amplified by tiny bones (hammer, anvil, stirrup) in the middle ear, which then move fluid in the snail-shaped cochlea (inner ear).
- This fluid motion bends hair cells that convert the vibrations into electrical signals, sent via the auditory nerve to the brain, which interprets them as sound
How is the ear responsible for balance?
- Semicircular Canals: These three loops are oriented in different planes (horizontal, vertical).
When you turn your head, fluid inside the canals moves, bending tiny hair cells within them. - These hair cells send signals to your brain about the speed and direction of rotation.
- Otolith Organs (Utricle & Saccule):
These organs contain calcium crystals (otoliths) resting on a gelatinous layer with hair cells. - Gravity makes these crystals shift, bending the hair cells to tell your brain your head’s position relative to gravity and detect linear acceleration (like going up in an elevator).
Brain Integration:
The brain receives these messages from the inner ear.
It combines this sensory input with visual cues (what you see) and proprioception (your body’s sense of itself).
This integrated information allows your brain to coordinate muscles and keep you upright and stable.
Homeostasis
Homeostasis is the vital process where living organisms maintain a stable internal environment (like temperature, pH, and water balance) despite external changes, ensuring cells have optimal conditions for survival through self-regulating adjustments, primarily using negative feedback loops to counteract disruptions and keep vital functions balanced, like shivering to warm up or sweating to cool down.
Negative feedback
The most common mechanism; a change triggers a response that opposes the change, bringing the system back to normal (e.g., high blood sugar triggers insulin release to lower it).
Examples of homeostasis in the body
- Thermoregulation: Sweating when hot, shivering when cold.
- Blood Glucose: Insulin and glucagon balancing sugar levels.
- Blood Pressure: Adjustments to maintain stable flow.
- Hydration: Regulating water content.
Give the levels of organisation
cell > tissue > organ > organ system > organism
What are the four types of tissue?
- epithelial
- muscle
- connective
- nervous
Epithelial tissue (epithelium)
Epithelial tissue (epithelium) forms protective sheets covering body surfaces, lining cavities, and making up glands, functioning in protection, absorption, secretion, filtration, and sensation. Key features include tightly packed cells, polarity (apical/basal surfaces), avascularity (no blood vessels), and rapid regeneration, with nourishment coming from underlying connective tissue. It’s classified by cell layers (simple/stratified) and shape (squamous, cuboidal, columnar)
Muscle tissue
Muscle tissue is one of the body’s four primary tissue types, specialized for contraction, and is categorized into three main kinds: skeletal (voluntary movement, striated), cardiac (heart muscle, striated, involuntary), and smooth (organs/vessels, non-striated, involuntary). These tissues are made of myocytes (muscle cells) containing proteins like actin and myosin, which slide past each other to generate force, allowing for movement, organ function, and posture.
Skeletal muscle
Location: Attached to bones.
Appearance: Striated (striped) with long, cylindrical, multinucleated cells.
Control: Voluntary (conscious control).
Function: Body movement, heat production, organ protection.
-
Basic Chemistry43
-
Microbiology57
-
Enzymology23
-
Cell metabolism25
-
Introduction to genetic traits45
-
Cell Biology20
-
Protein synthesis and cell division69
-
Special senses84
-
Blood components51
-
Blood groups25
-
Blood clotting42
-
The nervous system part 124
-
The nervous system part 222
-
Histology29
-
Anatomy of the respiratory system38
-
Acid-base balance85
-
The muscle64
-
Homeostasis17
-
The skin29
-
The Digestive System36
-
Excitable cells99
-
The liver33
-
Embryology24
-
Introduction to the renal system70
-
Introduction to organic molecules20
-
Overview of the cardiovascular and cardiac conduction systems65
-
Introduction to immunology23
-
Chemical and cellular events of acute inflammation74
-
Reproductive systems37
-
Physiology of pregnancy10
-
Skeletal system18
-
Physiology of ageing33
-
Revision A+P John28
-
Revision A+P Alex48
