4.1.1 cell structure

eukaryotes

plant and animal cells - cell membrane, cytoplasm

• genetic material enclosed in a nucleus

• membrane-bound organelles

prokaryotes

bacterial cells - much smaller

• cytoplasm, cell membrane surrounded by a cell wall

• genetic material is NOT enclosed in a nucleus (no true nuclues)

• single dna loop + 1 or more small rings of dna (plasmids)

• no membrane-bound organelles (like mitochondria or chloroplasts)

plasmids

small rings of dna that can replicate independently

can carry beneficial genes (such as those for antibiotic resistance)

can be transferred from one cell to another & allow bacterial cells to move genes from one cell to another

used in genetic engineering - allow genes to be inserted into bacteria

cytoplasm

liquid gel that organelles are in & where most of the chemical reactions take place

cell wall (plant and algal cells)

made of cellulose & strengthens the cell

nucleus

controls the activities of the cell + contains genetic material

chloroplasts

contain chlorophyll (absorb light)

photosynthesis occurs here

mitochondria

where aerobic respiration takes place and releases energy for the cell to use

permanent vacuole

filled with cell sap to keep the cell rigid for support

ribosomes

where protein synthesis occurs

cell membrane

controls the passage of substances into and out of the cell

function of root hair cell

absorb water and mineral ions from the soil

adaptations of root hair cells

• shape provides large surface area to increase uptake

• large permanent vacuole helps increase speed of water uptake by osmosis

• many mitochondria to provide energy for the active uptake of mineral ions

function of xylem cell

transport water and mineral ions from the roots to the rest of the plant

adaptations of xylem cells

• lignin cell walls to provide strength against the pressure of water

• form long, hollow tubes (as there are no top and bottom walls) - to allow continuous movement of water and mineral ions

function of phloem cells

transport sugar made in photosynthesis around the plant

adaptations of phloem cells

• perforated end walls (sieve plates) to allow sugar solution to pass through

• as phloem lack most organelles, they have companion cells (that have mitochondria) to provide them with energy

function of sperm cell

contains genetic information (from the father)

has to swim to reach the egg to fertilise it

adaptations of sperm cell

• long moving tail to swim - with lots of mitochondria to provide energy

• acrosome in the head contains digestive enzymes to break through the egg cell’s outer layer

• has a large nucleus containing half the genetic material

function of muscle cell

contract and relax for movement

adaptations of muscle cell

• special proteins that can slide over each other - muscle fibres contract

• contain glycogen (glucose stores) - broken down and used for respiration to release energy

• many mitochondria to release energy for muscle fibres to contract and relax

function of nerve cell

carry electrical impulses to send messages around the body

adaptations of nerve cells

• lots of dendrites to form connections to many nerve cells

• long thin axon which is like an electrical wire - carries the electrical impulse (covered in myelin sheath - insulates and speeds up the impulse)

• lots of mitochondria to provide energy