IB Biology (all topics)

• Exceptions to cell theory

  • Skeletal muscle fibers are larger/have many nuclei/are not typical cells
  • Fungal hyphae are (sometimes) not divided up into individual cells
  • Unicellular organisms can be considered acellular because they are larger than a typical cell/carry out all functions of life
  • Some tissues/organs contain large amounts of extracellular material e.g. vitreous humor of eye/ mineral deposits in bone/ xylem in trees/other example
• Extracellular component


  Plant cell wall/cellulose/interstitial matrix/basement membrane/glycoprotein/bone matrix

  
• Functions of extracellular components

  • Strengthens/supports the cell/plant (against gravity)
  • Prevents the entry of pathogens
  • Maintains the shape of plant cells
  • Allows turgor pressure/high pressure to develop inside the cell
  • Prevents excessive entry of water to the cell
  • Helps cells to stick together/adhere
  • Needed to hold cells/tissues together
  • Forms interstitial matrix / forms basement membrane to support single layers of cells
  • Forms (part of the) filtration membrane in the glomerulus
• Small cells have larger surface area to volume ratio

  Ratio decreases as size increases
• Importance of surface area to volume ratio

  • Surface area/membrane must be large enough to absorb nutrients/oxygen/substances needed
  • Surface area/membrane must be large enough to excrete/pass out waste products
  • Need for materials is determined by (cell) volume
  • Cell size is limited (by SA/Volume ratio)/cells divide when they reach a certain size
• Differentiation


  Development in different/specific ways
• Differentiation in multicellular organisms

  • Cells carry out specialized functions/become specialized
  • Cells have all genes/could develop in any way
  • Some genes are switched on/expressed but not others
  • Position/hormones/cell-to-cell signals/chemicals determine how a cell develops
  • A group of differentiated cells is a tissue
• Stem cells


  • Undifferentiated cells
  • Embryo cells are stem cells
  • Can differentiate in many/all ways / are pluripotent/totipotent
  • Differentiation involves expressing some genes but not others
  • Can be used to repair/replace tissues/heal wounds
• Organelles found in the cytoplasm of plant cells

  • Rough endoplasmic reticulum
  • Free ribosomes
  • Golgi apparatus
  • Mitochondrion
  • Chloroplast
  • Vacuole
  • Nucleus
  • Lysosome
  • Smooth endoplasmic reticulum

  
• Functions of organelles


  • Lysosome: hydrolysis/digestion/break down of materials (macromolecules)
  • Golgi apparatus: synthesis/sorting/transporting/secretion of cell products
  • Rough endoplasmic reticulum: site of synthesis of proteins (to be secreted)/ intracellular transport of polypeptides to Golgi apparatus
  • Nucleus: controls cells activities/mitosis/replication of DNA/transcription of DNA (to RNA)/directs protein synthesis
  • Mitochondrion: (aerobic) respiration/generates ATP
• Differences between plant and animal cells

  • Plant cells have cell walls, animals do not
  • Plant cells have plastids/ chloroplasts, animals do not
  • Plant cells have a large central vacuole, animals do not
  • Plant cells store starch, animal cells store glycogen
  • Plant cells have plasmodesmata, animal cells do not
  • Plant cells have fixed shape / more regular shape
  • Animal cells have centrioles, plant cells do not
  • Animal cells have cholesterol in the cell membrane, plant cells do not
  • Animal cells are more rounded

  
• Differences between prokaryotic and eukaryotic cells

  • Prokaryotic cells have naked/loop of DNA, eukaryotic cells have DNA associated with protein/histones/nucleosomes/DNA in chromosomes
  • Prokaryotic cells have DNA located in cytoplasm/nucleoid/no nucleus, eukaryotic cells have DNA located within a nucleus/nuclear membrane
  • Prokaryotic cells lack membrane bound organelles, eukaryotic cells have membrane bound organelles
  • Prokaryotic cells have 70S Ribosomes, eukaryotic cells have 80S Ribosomes
  • Prokaryotic cells have same plasma membrane structure as Eukaryotic cells
  • Prokaryotic cell walls are composed of peptidoglycan/not composed of cellulose/not composed of chitin, eukaryotic cell walls are composed of cellulose/chitin/not composed of peptidoglycan
  • Prokaryotic cells lack mitochondria, eukaryotic cells have mitochondria
  • Prokaryotic cells have pili, eukaryotic cells lack pili
  • Prokaryotic cells sometimes have plasmids, eukaryotic cells lack plasmids
  • Prokaryotic flagella are solid, eukaryotic flagella are flexible/membrane-bound
• Structure of a cell membrane

  • Phospholipids with hydrophillic (heads) and hydrophobic (tails)
  • Phospholipid bilayer
  • Proteins in the bilayer
  • Transmembrane and peripheral/extrinsic proteins
  • Glycoproteins
  • Cholesterol
  • Glycolipids

  
• How phospholipid structure and properties maintain cell membrane structure

  • Hydrophobic tail/hydrophilic head
  • Phospholipids form a bilayer with heads facing outside and tails facing inside
  • Phospholipids held together by hydrophobic interactions
  • Phospholipid layers stabilized by interaction of hydrophilic heads and surrounding water
  • Phospholipids allow for membrane fluidity/ flexibility
  • Fluidity/ flexibility helps membranes to be (functionally) stable
  • Phospholipids with short fatty acids/ unsaturated fatty acids are more fluid
  • Fluidity is important in breaking and remaking membranes (e.g. endocytosis/ exocytosis)
  • Phospholipids can move about/ move horizontally/ "flip flop" to increase fluidity

  
• Vesicles


  • Membrane bound packages/droplets
  • Formed by pinching off/budding off a piece from a membrane
  • Can carry proteins
• Role of vesicles in transportation

  1. Rough ER synthesizes proteins

  2. Proteins enter/accumulate inside the ER

  3. Transported to Golgi apparatus for processing

  4. Targeted to/transported to specific cellular organelles

  5. Fuse with membrane of organelle so contents of vesicle join the organelle

  6. Transported to the plasma membrane

  7. Fuses with plasma membrane releases/secretes contents

  8. Exocytosis

  
• Passive vs active transport

  • Passive: oxygen across alveoli / other example
  • Active transport: glucose absorption in ileum / other example
  • Passive: diffusion / osmosis / facilitated diffusion
  • Active transport: ion pumps / exocytosis / pinocytosis / phagocytosis
  • Passive: does not require energy
  • Active transport: requires energy/ATP
  • Passive: down concentration gradient
  • Active transport: against concentration gradient
  • Passive: no pumps needed
  • Active transport: requires protein pumps
• Exocytosis


  1. Vesicles carry material to plasma membrane

  2. Vesicle fuses with membrane

  3. (By joining of) phospholipid bilayers

  4. Aided by the fluidity of the membrane

  5. Material released/expelled from the cell

  6. Membrane flattens

  7. Example: exocytosis of neurotransmitter / exocrine secretion/endocrine secretion / hormone secretion / release of cortical granules

  
• Processes in interphase


  1. DNA replication

  2. DNA transcription

  3. Enzyme/ protein synthesis

  4. Biochemical reactions/ example of a biochemical reaction

  5. Cell respiration

  6. Growth

  7. Organelles replicated
• Relationship between amino acids and dipeptides

  1. Condensation / dehydration synthesis: water produced (when two amino acids joined)

  2. Hydrolysis: water needed to break bond

  3. Dipeptide --> amino acids - hydrolysis occurs

  4. Amino acids --> dipeptide - condensation occurs
• UNIT 2.2: WATER
• Properties of water


  • Thermal
  • Cohesive
  • Solvent
• Cell Division


  1. DNA replication

  2. DNA transcription

  3. Enzyme/protein synthesis

  4. Biochemical reactions/example of a biochemical reaction

  5. Cell respiration

  6. Growth

  7. Organelles replicated
• Relationship between amino acids and dipeptides

  1. Condensation/dehydration synthesis: water produced (when two amino acids joined)

  2. Hydrolysis: water needed to break bond

  3. Dipeptide --> amino acids - hydrolysis occurs

  4. Amino acids --> dipeptide - condensation occurs
• Water


  • High specific heat capacity
  • Large amount of heat causes small increase in temperature
  • High latent heat of vaporization
  • Large amount of heat energy needed to vaporize/evaporate
  • Hydrogen bonds between water molecules make them cohesive/stick together
  • Polar molecules make water a good solvent
• Significance of water to living organisms

  • Surface tension - allows some organisms to move on water's surface
  • Polarity/capillarity/adhesion - helps plants transport water
  • Excellent solvent - capable of dissolving substances for transport
  • Excellent thermal properties (high heat of vaporization) - excellent coolant
  • Ice floats - lakes/oceans do not freeze, allowing life under the ice
  • Buoyancy - supports organisms
  • Structure - turgor in plant cells/hydrostatic pressure
  • Habitat - place for aquatic organisms to live
• Carbohydrates for energy storage in animals

  • Stored as glycogen (in liver)
  • Short-term energy storage
  • More easily digested than lipids so energy can be released more quickly
  • More soluble in water for easier transport
• Lipids for energy storage in animals

  • Stored as fat
  • Long-term energy storage
  • More energy per gram than carbohydrates
  • Insoluble in water so less osmotic effect
• Functions of lipids


  • Energy storage/source of energy/respiration substrate
  • (Heat) insulation
  • Protection (of internal organs)
  • Water proofing/cuticle
  • Buoyancy
  • Structural component of cell membranes
  • Electrical insulation by myelin sheath
  • (Steroid) hormones
  • Glycolipids acting as receptors
• Functions of proteins


  • Storage - zeatin (in corn seeds)/casein (in milk)
  • Transport - hemoglobin/lipoproteins (in blood)
  • Hormones - insulin/growth hormone/TSH/FSH/LH
  • Receptors - hormone receptor/neurotransmitter receptor/receptor in chemoreceptor cell
  • Movement - actin/myosin
  • Defense - antibodies/immunoglobin
  • Enzymes - catalase/RuBP carboxylase
  • Structure - collagen/keratin/tubulin/fibroin
  • Electron carriers - cytochromes
  • Pigments - rhodopsin
  • Active transport - sodium potassium pumps/calcium pumps
  • Facilitated diffusion - sodium channels/aquaporins
• Structure of proteins


  • Chain of amino acids/sequence of amino acids
  • 20 different amino acids
  • Linked by peptide bonds
  • Secondary structure formed by interaction between amino and carboxyl/-NH and -C=O groups
  • Hydrogen bonds formed
  • α-helix formed/polypeptide coils up
  • Or ß-pleated sheet formed
  • Tertiary structure is the folding up of the polypeptide
  • Stabilized by disulfide bridges/hydrogen/ionic/hydrophobic bond
  • Quaternary structure is where several polypeptide subunits join
  • Conjugated proteins are proteins which combine with other non-protein molecules

  
• Reasons for converting lactose to glucose and galactose during food processing


  • Allows people who are lactose intolerant/have difficulty digesting lactose to consume milk (products)
  • Galactose and glucose taste sweeter than lactose reducing need for additional sweetener (in flavored milk products)
  • Galactose and glucose are more soluble than lactose/gives smoother texture/reduces crystallization in ice cream
  • (Bacteria) ferment glucose and galactose more rapidly (than lactose) shortening production time (of yoghurt/cottage cheese)
• Reasons for using lactase at relatively low temperatures

  • Less denaturation/enzymes last longer at lower temperatures
  • Lower energy costs/less energy to achieve 5 °C compared to 48 °C
  • Reduces bacterial growth/reduces (milk) spoilage
  • To form products more slowly/to control the rate of reaction
• How enzymes catalyze reactions

  1. They increase rate of (chemical) reaction

  2. Remains unused/unchanged at the end of the reaction

  3. Substrate joins with enzyme at active site

  4. To form enzyme-substrate complex

  5. Active site/enzyme (usually) specific for a particular substrate

  6. Enzyme binding with substrate brings reactants closer together to facilitate chemical reactions (such as electron transfer)

  7. Making the substrate more reactive
• Effect of pH on enzyme activity

  • Enzymes have an optimal pH
  • Lower activity above and below optimum pH
  • Too acidic/base pH can denature enzyme
  • Change shape of active site/tertiary structure altered
  • Substrate cannot bind to active site/enzyme-substrate complex cannot form
  • Hydrogen/ionic bonds in the enzyme/active site are broken/altered
• Structure of the DNA double helix

  • Subunits are nucleotides
  • One base, one deoxyribose and one phosphate in each nucleotide
  • Four different bases - adenine, cytosine, guanine and thymine
  • Nucleotides linked up with covalent/phosphodiester bonds
  • Two strands linked together by base to base, A to T and G to C, with hydrogen bonds
  • Antiparallel strands
  • Double helix

  
• Genetic code


  • Composed of mRNA base triplets called codons
  • 64 different codons
  • Each codes for the addition of an amino acid to a growing polypeptide chain
  • Degenerate - more than one codon can code for a particular amino acid
  • Universal - same in almost all organisms
  • AUG is the start codon
  • Some codons code for the end of translation
• Advantages and disadvantages of the universality of the genetic code to humans

  • Genetic material can be transferred between species/between humans
  • One species could use a useful gene from another species
  • Transgenic crop plants/livestock can be produced
  • Bacteria/yeasts can be genetically engineered to make a useful product
  • Viruses can invade cells and take over their genetic apparatus
  • Viruses cause disease
• Differences between RNA and DNA

  • DNA is double-stranded while RNA is single-stranded
  • DNA contains deoxyribose while RNA contains ribose
  • The base thymine found in DNA is replaced by uracil in RNA
  • One form of DNA (double helix) but several forms of RNA (tRNA, mRNA and rRNA)

  
• Roles of mRNA, tRNA and ribosomes in translation

  1. mRNA with genetic code/codons

  2. tRNA with anticodon

  3. tRNA with amino acid attached

  4. Ribosome with two sub-units

  5. mRNA held by ribosome

  6. Start codon

  7. Two tRNA molecules attached with mRNA on ribosome

  8. Peptide bond between amino acids on tRNA

  9. Polypeptide forms

  10. Continues until a stop codon is reached

  11. Polypeptide is released