mock unit 1

nucleus

contains DNA, controls cell activities

cell membrane

controls entry/exit of substances

mitochondria

site of aerobic respiration, release energy

ribosomes

site of protein synthesis

cell wall

made of cellulose, provides strength/support

chloroplasts

contain chlorophyll, site of photosynthesis

vacuole

large permanent, stores cell sap, maintains turgor pressure

chromosomal DNA

single loop, controls cell activities (no nucleus)

plasmid DNA

small rings, carry extra genes (e.g., antibiotic resistance)flagella

acrosome (sperm cell)

contains enzymes to digest egg cell membrane

haploid nucleus (sperm cell)

half chromosomes for fertilisation

mitochondria (sperm cell)

many in midpiece) – provide ATP for movement

tail

flagellum for swimming

nutrients in cytoplasm (egg cell)

provide energy/food for developing embryo

haploid nucleus

half chromosomes for fertilisation

changes in cell membrane after fertilisation

block other sperm prevent polyspermy

many cilia on surface

beat to move mucus/eggs/dust (e.g., airways trap pathogens, oviduct moves egg)

Light microscopes

limited resolution, see cells but not organelles clearly

electron microscopes

use electrons, much higher resolution and magnification, show detailed organelles which enabled discovery of organelle roles

what are enzymes?

biological catalysts

lock and key model

active site has specific 3D shape complementary to substrate which fits exactly into active site to form an enzyme-substrate complex, reaction occurs and products are released

enzyme specificity

only complementary substrate fits (shape determined by amino acid sequence)

enzyme denaturation: extreme pH/high temp

breaks bonds holding enzyme shape causing; active site to change shape making it no longer complementary to substrate, the substrate cannot bind so enzyme becomes denatured

how does temperature affect enzyme activity?

at a low temperature there is low kinetic energy, few collisions, as temperature increases there more kinetic energy and collisions causing faster enzyme-substrate complexes

temperature what happens at the optimum?

rate increases to optimum and above the optimum, enzyme denatures (active site shape changes) so rate decreases sharply to zero

how does substrate concentration affect enzyme activity?

low substrate leads few collisions and low rate while increase substrate leads to more collisions, more complexes and rate increases

substrate: what happens when it gets high?

at high substrate, all active sites occupied (saturation) leading to rate plateaus

how does pH affect enzyme activity

each enzyme has optimum pH, the wrong pH changes ionisation of amino acids and breaks bonds causing active site shape to alter leading to reduced activity or denaturation so rate decreases

explain the importance of enzymes as biological catalysts

enzymes speed up reactions without being used up; essential for: synthesis of macronutrients and breakdown into sugars/amino acids/fatty acids + glycerol which allow life processes at body temperature

explain how the energy contained in food can be measured using calorimetry

burn food sample in calorimeter → heat released warms water; energy (kJ/g) = (mass water × temp rise × 4.2) / mass food burned; measures chemical energy in bonds

diffusion

net movement high to low concentration (passive, no energy)

!osmosis

diffusion of water acrosspartially permeable membrane, high to low water potential (passive, e.g., root hairs)

active transport

low to high concentration against gradient (requires energy/ATP, carrier proteins, e.g., mineral ions in roots, glucose in gut)