Science B1

Prokaryotes are single celled organisms

Eukaryotes are complex, animal and plant cells. eukaryotes are made of eukaryotic cells

• nucleus - contains genetic material, controls the cell
• cytoplasm - gel-like substance, where chemical reactions occur
• cell membrane - holds cell together, controls what goes in and out
• mitochondria - reactions for aerobic respiration here, respiration transferres energy for cells to work
• ribosomes - proteins are made in the cell
• cell wall - made of cellulose, supports and strengthens the cell
• permanent vacuole - cell sap (sugar and salts)
• chloroplasts - chlorophyll, makes food through photosynthesis
• cell wall, cell membrane, cytoplasm
• small rings of dna called plasmids
• no chloroplasts or mitochondria
• bacterial cells dont have a true nucleus - single circular strand of dna floating freely

Actual object size = Image size/magnification I=AxM

Practical:

• 1. prepare your slide - add drop of water, specimen, iodine then coverslip
• 2. clip slide onto stage, select lowest power objective lens, use coarse adjustment knob, adjust focus with fine adjustment knob
• 3. draw observations (in pencil), write title, magnification, label important features

Electron microscopes have a higher resolution

Iodine is needed to stain the sample to highlight objects in the cell by adding colour

Cells differentiate to become specialized - become specialized for the job

• develop different subcellular structures to be able to carry out specific functions
• in most animal cells, the ability to differentiate is lost at an early stage, after they become specialized. lots of plant cells dont loose this ability
• cells that differentiate in mature animals are mainly used for repairing and replacing cells such as skin or blood cells
• unindifferentiated cells are called stem cells.

Sperm cells: reproduction

• male DNA to the female DNA
• long tail and streamlined head to help swim to the egg
• lots of mitochondria to provide energy
• enzyemes to digest through egg cell membrane

Nerve cells: rapid signalling

• long and have branched connections

muscle cells: contraction

• long (space to contract)
• lots of mitochondria to generate the energy

root hair cells: absorbing water and minerals

• long hairs stick into the soil (large surface area)

phloem and xylem cells: transporting substances

• long tubes joined end to end
• xylem cells are hollow
• phloem have very few subcellular structures so stuff can flow through them

Diffusion is the movement of particles from an area of high concentration to an area of low concentration

• occurs in solutions and gases-because are free to move about randomly
• the bigger the concentration gradient (difference in concentration), the faster the diffusion rate
• the higher the temperature, the faster the diffusion rate because the particles have more energy, so move around faster

Cell membranes:

• hold the cell together but let stuff in and out as well
• dissolved substances can move in and out by diffusion
• small molecules (oxygen, glucose, amino acids, water) can fit
• big molecules (starch, protein) cant fit
• the larger the surface area the faster the diffusion rate, because more particles can fit through at once

osmisis is the movement of water across a partially permeable membrane from aan area of high concentration to an area of low concentration

• a type of diffusion (passive) just is of water

Practical:

• cut potato into equal cylinders, weigh and record
• leave them 24hours in solutions of sugar (eg 0.2mol/dm³, and pure water)
• take out and dry, weigh and record
• if the cylinders have drawn in water by osmosis they will have increased in mass
• if water has been drawn out they will have decreased in mass
• dependent variable --> potato mass
• independent variable --> concentration of sugar solution
• control variables --> volume of solution, temperature, time, type of sugar used etc
• if potato was not fully dried the excess water will give a higher mass

substances move from an area of LOW concentration to an area of high concentration across a permeable membrane

• across a concentration gradient so requires energy from mitochondria

Root hair cells:

• plants need mineral ions for healthy growth
• the concentration of minerals is usually higher in the root hair than in the soil
• therefore root hair cells cant use diffusion to take up minerals

active transport happens in humans eg. taking glucose from the gut and kidney tubules

• lower concentration of nutrients in the gut to a higher concentration of nutrients in the blood
• glucose, taken from the gut can be taken into the bloodstream and transported to cells to be used for respiration

Exchange surfaces:

• the larger the surface area to volume ratio, the better the exchange rate
• adapted to maximise effectiveness
  • thin membrane - short distance to diffuse
  • large surface area - lots can diffuse at once
  • animals have lots of blood vessels - remove from blood quicker
  • gas exchange in animals (alveolli) are ventilated - air moves in and out

In the lungs:

• job is to transfer oxygen to the blood and remove waste carbon dioxide
• lungs contain millions of little air sacs called alveoli
  • enormous surface area
  • moist lining for dissolving gases
  • very thin walls
  • good blood supply

Small intestines have millions of villi

• single layer of surface cells
• good blood supply

Plants:

• carbon dioxide diffuses into the air spaces within the leaf then diffuses into the cells where photosynthesis occurs
• the underleaf is covered in holes called stomata
• oxygen and watervapour (waste products) diffuse out of the stomata (water vapour is lost all over the leaf but mainly from the stomata)
• the size of the stomata are controlled by guard cells - they close if the plant is loosing too much water - otherwise they will wilt as the roots are not replacing the water
• the flattened shape increases surface area
• the walls of the cells also exchange substances. the air spaces increase the surface area

Fish:

• water(containing oxygen) enters the fish through mouth, oxygen diffuses into the blood, carbon dioxide diffuses out into the water, water then passes out the gills
• gills are made of gill filaments, and lamellae on them - larger surface area
• lamellae have lots of blood capillaries, and they have thin surface layer of cells 
• blood flows through lamellae one way, and water the other: large concentration gradient between water and blood, concentration of oxygen in water is higher than in blood

Chromosomes:

• found in nucleus, the genetic material/information
• made of coiled up DNA molecules
• large number of genes, these control characteristics (eg hair colour)
• body cells have 2 copies of chromosomes, one from mother, one from father
• 23 pairs of chromosomes

Mitosis:

• stage of cell cycle when the cell divides
• multicellular organisms use mitosis to grow or replace cells that have been damaged
• growth and DNA replication:
  • DNA spread out in long strings, cell has to grow and increase amount of subcellular structures then duplicates DNA (forms x shape)
• mitosis
  • cell fibres pull apart lined up chromosomes, they then go to opposite ends of the cell
  • membrane form around sets of chromosomes then cytoplasm and cell membrane divide
  • new "daughter cells" are identical to parent cell

• can turn into any type of cell - depending on given instructions
• found in early human embryos 
• adults have stem cells in bone marrow, but can only turn into certain cells such as blood cells
• stem cells can be grown in a lab to produce clones (genetically identical) then made to differentiate into specialized cells to use in medicine or research

• medicine uses adult stem cells to cure disease eg bone marrow of healthy person replaces faulty blood cells in sick patient
• embryonic stem cells can replace fautly cells - make insulin producing cells for diabetics, nerve cells for people paralysed by spinal injuries
• therapeutic cloning ensures stem cells for patients have same genes so not rejected by body
• risks include stem cells contaminated with virus in lab, making patient ill

• people are against stem cell research becuase it distroys a potential human life 
• others think curing patients is more important than rights of embryos
• embryos used in research are unwanted, from fertility clinics, but still campaigners want other sources of stem cells to be found. research allowed in UK if follows strict guidelines

Plants:

• found in meristems (where growth occurs)
• throughout entire life, meristem cells can differetiate into any type of plant cell
• these stem cells can produce clones quickly and cheaply
• can be used to grow more plants of rare species
• can grow crops of identical plants that have desired features eg disease resistant

Cells --> tissues --> organs --> organ systems 

cells - basic building blocks

tissues -

• group of similar cells working together to carry out a particular function
• eg muscular tissue which contracts to move what its attached to

organs -

• group of different tissues working together to carry out a particular function
• eg stomach is made of musclar tissue, glandular tissue and epithelial tissue

organ systems -

• a group of organs working together to carry out a particular funtion
• eg diestive system made of glands, stomach, small and large intestine, liver etc. 

Breaks down and absorbs food:

• 1st: Salivary glands - produce amylase enzyme in the saliva
• 2nd: Gullet/oesophagus
• 3rd: Stomach - pummels food with muscular walls, produces protease enzyme, pepsin, produces hydrochloric acid to kill bacteria and give the right pH for protease to work (2)
• Liver - produces bile which neutralizes stomach acid and emulsifies fat
• Gall bladder - bile is stored before being released into the small intestine
• Pancreas - produces protease, amylase and lipase which are released into small intestine
• 4th: Small intestine - produces protease, amylase and lipase to complete digestion, digested food is absorbed into the blood
• Large intestine - excess water is absorbed from food
• Rectum - faeces (indigestable food) are stored before leaving

• 1st break up food using pestle and mortar
• add distilled water and stir to dissolve some food
• filter the solution to get rid of solid bits

Benedict's test for reducing SUGAR:

• prepare food sample, 75⁰C water bath, add 10 drops of benedict's solution, put in water bath for 5 mins
• if food sample contains reducing sugar, will turn from blue to green, yellow or brick red

Iodine solution test for STARCH:

• prepare food sample, add a few drops of iodine and shake
• if starch is present, solution will change from browny-orange to black or blue-black

Biuret test for PROTEIN:

• prepare sample, add 2 cm³ of biuret solution and shake
• if protein is present, solution will change from black to pink or purple

Sudanīīī to test for LIPIDS:

• prepare sample (dont filter), add 3 drops of sudanīīī and shake
• if lipids are present the mixture will separate with the top layer red

• biological catalysts
• a catalyst increases the speed of a reaction with out being changed or used up
• enzymes are large proteins (chains of amino acids)
• enzymes only speed up wanted reactions (temperature would increase all)
• enzymes have special shapes so the substrate will fit perfectly into the active site
• enzymes need the right pH and temperature
• a higher temperature increases the rate AT FIRST. any higher and the enzyme denatures (breaks down and the active site shape changes)
• the pH will denature enzymes if it is too high or low (ususally pH7 but pepsin breaks down protein in the stomach and has optimum pH of 2.)

Practical:

• amylase catalyses breakdown of starch to maltose. 
• 1) put iodine into every tile of spotting tile
• 2) set up bunsen burner, tripod and guaze. put beaker of water on the tripod and heat to 35⁰
• 3) keep temp consistant. add 1cm³ amylase and 1 cm³ buffer solution (pH5) put test tube in water for 5 mins. add 5cm³ starch. mix and start timer. every 30 seconds put a sample into the spotting tile
• 4) repeat for different pHs. when iodine is browny-orange starch is no longer present

• rate of reaction:
• Rate = 1000/time (s‾1)
• Carbohydrase (amylase) breaks down carbohydrates (starch) into simple sugars (maltose)
• amylase is made in the salivary glands, pancreas, and small intestine
• Protease breaks down proteins into amino acids
• protease is made in the stomach (pepsin), the pancreas and small intestine
• Lipase breaks down lipids (fat) into glycerol and fatty acids
• lipase is made in the pancreas and the small intestine
• molecules are too big to pass through the walls of the digestive system so digestive enzymes break them down. smaller, soluble molecules can easily pass through and be absorbed into the bloodstream
• Bile produced in the liver, stored in the gall bladder, released into the small intestine, neutralizes stomach acid and makes it alkaline. enzymes in the small intestine work better in alkaline conditions
• it emulsifies fat (breaks it into smaller, tiny droplets, so it has a bigger surface area for the lipase to work, speeding up digestion

• Oxygen is taken in and sent to cells to use for respiration. also waste carbon dioxide is removed
• air goes ---> down trachea ---> bronchus ---> bronchiole ---> alveoli

Circulatory system: carries food and oxygen to the body cells and removes waste

• 1st system: right ventricle pumps deoxygenated blood to the lungs. returns to heart full
• 2nd system: left ventricle pumps oxygenated blood to the body cells. returns empty to heart
• coronary arteries branch off the aorta and supply the heart cells
• the heart has valves to prevent the blood from flowing backwards
• the heart has four chambers, the left and right ventricle and the left and right atrium. the ventricle is at the bottom
• the pulmonary artery brings in oxygenated blood and the aorta takes it away
• the vena cava brings in deoxygenated blood and the pulmonary artery takes it away
• the muscle is thicker on the left side because the oxygenated blood is a higher pressure

Blood vessels:

• Arteries: pumps oxygenated blood away from the heart at high pressure so walls are strong and elastic. the walls are thin compared to the size of the lumen. they have layers of muscle and elastic fibres to allow them to stretch
• Capillaries: arteries branch into them so they are tiny. they are thin (only 1 cell thick) so they can diffuse the blood to the cells quicker
• Veins:capillaries branch back into veins. lower pressure so walls are not thick. they have a bigger lumen and valves to keep the blood flowing despite low pressure

Blood:

• red blood cells carry oxygen. they have a biconcave shape to increase the surface area and no nucleus to make more room for oxygen. haemoglobin binds to the oxgen becoming oxhaemoglobin
• white blood cells defend against infectionby producing antibodies, antitoxins or by changing shape to counteract harmful pathogens
• platelets clot blood. they are fragments of cells with no nucleus. lack can cause blood leaks
• plasma is a liquid that carrys everything else as well as glucose, amino acids, co2, urea, hormones, proteins, and antibodies and toxins

coronary heart disease is when coronary arteries get blocked by layers of fatty material - causing lack of oxygen, and a heart attack

• stents keep arteries open
• statins reduce cholesterol in the blood (drugs). they slow down the rate of fatty material building up
  • advangages: reduces bad cholesterol and risk of heart attack, and increases good cholesterol
  • disadvantages: drug has bad side effects eg. headaches, liver damage and effect is not instant

an artificial heart can he used if a heart donor is not available

faulty heart valves can be replaced with arteficial or donors

artificial blood can be used. a substitution (eg saline - a salt solution) can replace the function of the lost red blood cells, and give time for the patient to preduce new red blood cells

Pathogens: microorganisms that cause disease. collective name for bacteria, fungi and virus

• bacteria are very small cells that produce toxins (poisons) that damage your cells. thy reproduce very rapidly
• viruses are not cells: they reproduce quickly inside body cells then the cell will burst. this damage makes you feel ill
• fungi grows and penetrates human skin and surface of plants causing disease. they can produce spores which spread to other plants
• pathogens can be spread by 
  • water - (cholera - bacterial)
  • Air - coughs and sneezes (flu - virus)
  • Direct contact - by touching contaminated surfaces including skin (athletes foot - fungal)
• Viral diseases:
  • measles is spread by air and is a red skin rash and fever. it can be very serious and fatal if there are complications. most people are vaccinated when young

• • HIV is sexually transmitted by exchanging bodily fluid. it initially causes flu-like symptoms during the first few years when no symptoms are yet caused, the virus can be stopped with antiretroviral drugs. the virus attacks the immune system so if it is damaged the body cant cope with other diseases. this is called AIDS
  • TMV (tobacco mosaic virus) affects many species of plants. it causes a mosaic pattern on the leaves (and discolouring) meaning the photosynthesis rate drops, affecting growth
• Fungal diseases:
  • Rose black spot causes purple or black spots on the leaves of roses. the leaves then turn yellow and drop off meaning less photosynthesis so less growth. it can spread through water or by wind and can be treated by fungicides or burning affected leaves
• Protist:
  • a protist is just a carrier of the disease but dont get it itself
  • malaria is caused by a protist - a mosquito. malaria is passed on from infected victim to mosquito to another healthy victim who gets malaria. it is recuring episodes of fever and can be fatal. the spread can eb stopped by stopping mosquitos from breeding, insecticides and mosquito nets

• Bacterial diseases:
  • salmonella causes food poisoning
  • symptoms are fever, stomach cramps, vomiting and diarrhoea. it is produced by toxins and caught from contaminated food such as prepared in unhygienic conditions. in UK poultry are given vaccination against salmonella
  • gonorrhoea is a sexually transmitted disease
  • symptoms are pain when urinating or thick yellow//green discharge. originally treated with penicillin but now bacteria have become resistant. prevention of spread can be with antibiotics or condoms

Spread of disease can be reduced by

First defence system:

• skin
• nose hair and mucus
• cilia
• ear wax
• hcl in the stomach

Second defence system:

• body produces white blood cells:
  • produce antibodies that lock onto antigens
  • produce antitoxins that counteract toxins
  • white blood cells engulf pathogens (phagocytsis)

Vaccination:

• injects dead pathogens so the body can prepare to fight live ones if and when they come

Vaccination

• pros
  • controls once common diseases
  • epidemics can be prevented
• cons
  • dont always give immunity
  • can produce reactions or give side effects

Drugs:

• painkillers relieve symptoms 
• antibiotics kill/prevent growth of bacteria
• but bacteria can be come resistant by changing - doctors make sure they avoid over-prescribing
• 1) first the new drug is tested on human cells and tissues
• 2) the drug is tested on live animals
• 3) the drug is tested on healthy volunteers
• 4) the drug is tested on sick volunteers

• risk factors:
  • lifestyle (diet)
  • presence of substances (air pollution)
• factors directly causing disease)
  • smoking ---> cardiovascular disease, lung disease and cancer. damages walls of arteries and lining of lungs
  • obesity ---> type2 diabetes makes body less sensitive to insulin, increasing glucose levels
  • alcholism ---> liver disease, brain function. damages nerve cells
  • smoking and alcoholism when pregnant can cause health problems for the unborn baby
  • exposure to radiation (xray, sun) causes cancer
• Cancer: uncontrolled cell growth forming tumours. (not always cancerous
  • benign - tumour grows until no more room. doesnt invade other tissues. not cancerous
  • malignant - grows and spreads. cancerous
• Risk factors
  • smoking - lung, mouth, bowel, stomach, cervical
  • obesity - bowel, kidney, liver
  • UV exposure - skin 
  • viral infection - hepatitis B and C
  • susceptible genes - breast, ovarian

• organs like stems, roots and leaves
• tissues like epidermal, meristem, xylem and phloem, palisade mesophyll and spongy mesophyll
• leaves contain epidermal, mesophyll, xylem and phloem
  • epidermal --> waxy cutile, reduces water loss by evaporation
  • upper epidermis --> transparent so light can reach palisade layer
  • palisade layer --> chloroplasts - photosynthesize
  • xylem and phloem --> deliver water and nutrients and take away glucose. support structure
  • lower epidermis --> full of stomata which diffuse gases
  • air spaces in spongy mesophyll increase rate of diffusion

Phloem: translocation

• made of columns of elongated cells with pores in teh end walls to let cell sap flow. transport food (dissolved sugars) made in leaves to rest of plant. transport goes in both directions

Xylem: 

• made of dead cells joined end to end with no end wall. strengthened with lignin. carry water and minerals from roots to stem and leaves

• evaporation and diffusion of water from a plants surface (leaves)
• evaporation creates a slight shortage of water so more is drawn up from the roots through the xylem cells to replace it
• called transpiration stream
• is a side-effect of how leaves are adapted for photosynthesis. they have to have stomata so gases can be exchanged more easily

Transpiration rate is affected by:

• light intensity - brighter the light, higher the transpiration rate
• temperature - the warmer it is, higher the transpiration rate
• air flow - stronger the wind, higher the transpiration rate
• humidity - the drier the air, higher the transpiration rate

Guard cells

• kidney shape - opens and closes stomata - more on bottom because shadier, less water loss
• when plant has lots of water, guard cells fill, go plump, turgid, when is short become flaccid and close to stop too much water vapour from escaping. close at night to save water loss