GCSE Cells

Eukaryotic cells Animal and plant cells are eukaryotic. They have genetic material (DNA) that forms chromosomes and is contained in a nucleus. cell membrane: controls the movement of substances in and out of a cell Animal cell Plant cell nucleus: contains DNA mitochondria: where energy is released through respiration cell wall: made of cellulose, which strengthens the cell permanent vacuole: contains cell sap chloroplasts: contain chlorophyll to absorb light energy for photosynthesis ribosomes: site of protein synthesis cytoplasm: jelly-like substance, where chemical reactions happen Bacteria have the following characteristics: • single-celled • no nucleus – have a single loop of DNA • have small rings of DNA called plasmids • smaller than eukaryotic cells. cell wall cytoplasm cell membrane plasmid DNA rings – bacteria may have more than one of these bacterial DNA loop (no nucleus) flagellum Prokaryotic cells Cells in animals and plants differentiate to form different types of cells. Most animal cells differentiate at an early stage of development, whereas a plant’s cells differentiate throughout its lifetime. Specialised cell Function Adaptations sperm cell fertilise an ovum (egg) • tail to swim to the ovum and fertilise it • lots of mitochondria to release energy from respiration, enabling the sperm to swim to the ovum red blood cell transport oxygen around the body • no nucleus so more room to carry oxygen • contains a red pigment called haemoglobin that binds to oxygen molecules • flat bi-concave disc shape to increase surface area- to- volume ratio muscle cell contract and relax to allow movement • contains protein fibres, which can contract to make the cells shorter • contains lots of mitochondria to release energy from respiration, allowing the muscles to contract nerve cell carry electrical impulses around the body • branched endings, called dendrites, to make connections with other neurones or effectors • myelin sheath insulates the axon to increase the transmission speed of the electrical impulses root hair cell absorb mineral ions and water from the soil • long projection speeds up the absorption of water and mineral ions by increasing the surface area of the cell • lots of mitochondria to release energy for the active transport of mineral ions from the soil palisade cell enable photosynthesis in the leaf • lots of chloroplasts containing chlorophyll to absorb light energy • located at the top surface of the leaf where it can absorb the most light energy Specialised cells Light microscope Electron microscope uses light to form images uses a beam of electrons to form images living samples can be viewed samples cannot be living relatively cheap expensive low magnification high magnification low resolution high resolution Electron microscopes allow you to see sub-cellular structures, such as ribosomes, that are too small to be seen with a light microscope. To calculate the magnification of an image: magnification = image size actual size Microscopes L Comparing diffusion, osmosis, and active transport Diffusion Osmosis Active transport Definition The spreading out of particles, resulting in a net movement from an area of higher concentration to an area of lower concentration. Factors which affect the rate of diffusion: difference in concentration, temperature, and surface area of the membrane. The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane. The movement of particles from a more dilute solution to a more concentrated solution using energy from respiration. Movement of particles Particles move down the concentration gradient – from an area of high concentration to an area of low concentration. Water moves from an area of lower solute concentration to an area of higher solute concentration. Particles move against the concentration gradient – from an area of low concentration to an area of high concentration. Energy required? no – passive process no – passive process yes – energy released by respiration Examples Humans • Nutrients in the small intestine diffuse into the capillaries through the villi. • Oxygen diffuses from the air in the alveoli into the blood in the capillaries. Carbon dioxide diffuses from the blood in the capillaries into the air in the alveoli. • Urea diffuses from cells into the blood for excretion in the kidney. Fish • Oxygen from water passing over the gills diffuses into the blood in the gill filaments. • Carbon dioxide diffuses from the blood in the gill filaments into the water. Plants • Carbon dioxide used for photosynthesis diffuses into leaves through the stomata. • Oxygen produced during photosynthesis diffuses out of the leaves through the stomata. Plants • Water moves by osmosis from a dilute solution in the soil to a concentrated solution in the root hair cell. Humans • Active transport allows sugar molecules to be absorbed from the small intestine when the sugar concentration is higher in the blood than in the small intestine. Plants • Active transport is used to absorb mineral ions into the root hair cells from more dilute solutions in the soil. Make sure you can write a definition for these key terms. cell membrane cell wall chloroplast chromosome concentration cytoplasm dilute DNA eukaryotic gill filaments gradient magnification mitochondria nucleus partially permeable membrane passive process permanent vacuole plasmid prokaryotic resolution ribosome root hair cell stomata