B1 and B2 Flashcards
Eukaryotes
Eukaryotes are multicellular organisms made of eukaryotic cells
Eukaryotic cells
All have cell membrane, cytoplasm and genetic material enclosed in nucleus
Prokaryote
A single celled organism made of a prokaryotic cell
Nucleus
Contains genetic material that controls activities of the cell
Cytoplasm
Where most chemical reactions happen
Contains enzymes that control these reactions
Cell membrane
Holds cell together
Controls what goes in and out
Mitochondria
Where most reactions for aerobic respiration take place
Ribosomes
Where proteins made in cell
Cell wall
Made of cellulose, strengthens cell
Permanent vacuole
Contains cell sap, a weak solution of sugar and salts
Chloroplasts
Where photosynthesis occurs
Contain green substance - chlorophyll - absorbs light for photosynthesis
Bacteria cell
Cell membrane
Cell wall
Cytoplasm
No nucleus instead single circular strand of DNA floating freely
May contain 1 or more small rings of DNA - plasmids
No mitochondria
Light microscope
Use light and lenses to let us see individual cells and large sub-cellular structures Eyepiece Ocular lens (one in eyepiece) Coarse adjustment knob (bigger one) Fine adjustment knob Objective lenses Stage Light
Electron microscope
Use electrons to form an image
Higher magnification and resolution than light
Let us see internal structure of mitochondria and chloroplasts and ribosomes and plasmids
Resolution
Ability to distinguish between two points
Gives sharper image
Image size
Real size times Magnification
How to prepare slide to view onion cells
1) Add drop of water to middle of clean slide
2) Cut onion and separate into layers. Use tweezers to peel of some epidermal tissue from bottom of layer
3) Place epidermal tissue into water
4) Add drop of iodine solution to stain
5) Place cover slip on top - make sure no air bubbles
Differentiation
Process by which a cell changes to become specialised for its job
In most animal cells they can no longer differentiate after becoming specialised
Lots of plant cells can always differentiate
Sperm cells
Long tail to help swim
Lots of mitochondria to provide energy
Enzymes in head to digest through egg cell membrane
Nerve cells
Longs cells to cover more distance
Branched connections at end
Muscle cells
Long cells so space to contract
Lots of mitochondria for energy needed to contract
Root hair cells
Grow into long hairs that stick out into soil
Large surface area to volume ratio for absorbing mineral ions and water
Phloem and Xylem cells
Cell are long and joined end to end
Xylem are hollow
Phloem few sub cellular structures
So easy transport of food and water
Chromosomes
Coiled up lengths of DNA molecules
Body cells normally have two copies of each chromosome, 1 from mother and father
23 pairs of chromosomes in human cell
Growth and DNA replication
In a cell that is not dividing DNA spread in long strings
1) Cell grows and increases amount of sub-cellular structures - mitochondria and ribosomes
2) Duplicates DNA to form X-shaped chromosomes
3) Mitosis
Mitosis
1) Chromosomes line up at centre of cell and cell fibres pull them apart, 2 arms of each chromosome go to opposite ends of cell
2) Membranes form around each of the sets of chromosomes to become nuclei
3) Cytoplasm and cell membrane divide
Binary fission
Prokaryotic cells replicate by binary fission
1) Circular DNA and plasmids replicate
2) cell gets bigger and circular DNA strands move to opposite poles
3) cytoplasm begins to divide and new cell walls begin to form
4) Cytoplasm divides and 2 daughter cells produced, each has 1 copy of circular DNA but has variable number of plasmids
How to grow Bacteria in lab
Bacteria are cultured in a culture medium - contains carbohydrates, minerals, proteins and vitamins needed to grow
Culture medium can be a nutrient broth solution or solid agar jelly
Not kept above 25°C because harmful pathogens may grow
How to spread bacteria on agar jelly
Petri dish and culture medium must be sterilised
Use inoculating loops but pass through flame to sterilise
Lid should be lightly taped to stop bacteria entering but oxygen must be able to enter
Store upside down to stop condensation falling on agar
Will form visible colonies on surface
How to investigate effect of Antibiotics on binary fission
Leave small circles of paper soaked in antibiotic or antiseptic in agar
Do control just soaked in water
See how bacteria grows
Measure area of inhibition zone (where bacteria has not grown) after to see which is most effective
Difference between Embryonic stem cells and Adult stem cells
Embryonic stem cells can differentiate into any cell in human body
Adult stem cells found in bone marrow can only differentiate into certain cells - blood cells
Stem cells in plants
Stem cells found in meristems (where growth occurs)
Can differentiate into any type of plant cell
Can be used to make clones of plants
Diffusion
Spreading out of particles from an area of higher concentration to lower concentration
Can occur in gases and solutions
Diffusion in the cell membrane
Only small molecules can pass through the cell membrane - oxygen, glucose, amino acids, water
Big molecules can’t fit through - starch, proteins
The molecules move randomly but overall net movement from higher to lower concentration
Osmosis
Movement of water molecules across a partially permeable membrane from a region of high water concentration to low concentration
Practical to show osmosis
Experiment with potato chips and sugar solutions
Method for osmosis practical
Cut potato into identical cylinders
Get beakers with different concentrations of sugar from pure water to 1mol/dm3
Measure mass of each potato cylinder
Put cylinder in each beaker and leave for 24 hours
Take out each cylinder and dry then take mass
Results from osmosis practical
Calculate percentage in mass of each potato cylinder and plot on graph
Variables for osmosis practical
Dependent - chip mass
Independent - concentration of sugar solution
Control - volume of solution, temperature, time, type of sugar
Possible errors for osmosis practical
Potato cylinders not fully dried - mass increased
If water evaporates from beakers concentrations of solutions would change
Reduce errors by repeating experiment and calculating mean percentage change
Active transport
Movement of substances against the concentration gradient
Active transport in root hair cells
Concentration of minerals usually higher in root hair cell than in soil
Requires energy from respiration to absorb minerals
Active transport in intestine
Higher concentration of nutrients in blood than in intestine
When higher concentration of glucose and amino acids in intestine they diffuse naturally
If not need active transport to allow nutrients to go into blood
Surface area to volume ratios
Larger the organism the smaller surface area to volume ratio
Higher surface area to volume ratio means more exchanges can occur
How are exchange surfaces adapted
Thin membrane - short distance to diffuse
Large surface area - more substances can diffuse at once
In animals - lots of blood vessels - get substances in and out of blood
Gas exchange surfaces often ventilated
Gas exchange in lungs
Lungs need to transfer oxygen to blood and remove carbon dioxide
Adaptations of alveoli
Large surface area
Moist lining so easier for gases to dissolve
Thin walls
Good bloody supply from capillaries
Adaptations of villi
Increase surface area as protruding from small intestine
Single layer of surface cells
Network of capillaries
How gases move in a leaf
Carbon dioxide diffuses into air spaces in leaf - then into cells where photosynthesis occurs
Oxygen and water vapour diffuse out of leaf through stomata
Water vapour evaporates from cells inside leaf
Then escapes by diffusion
How leafs adapted for gas exchange
Flattened shape of leaf increases area of exchange surface
Underneath of leaf covered in stomata surrounded by guard cells to control loss of water
Air spaces inside leaf increase surface area of walls of cells to allow for more CO2 to enter
What gases are exchanged in gills
Oxygen diffuses from water into blood
Carbon dioxide from blood to water
Adaptation of gills
Each gills has lots of thin plates - gill filaments - large surface area
Gill filaments covered in lamellae - increase surface area
Lamellae - lots of capillaries, thin surface layer of cells
Blood flows through lamellae in one direction, water another - maintains high concentration gradient
