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Science biology

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Define eukaryotic cells

Eukaryotic (animal and plant) cells contain their genetic material - DNA enclosed in a nucleus

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275 questions
Define eukaryotic cells
Eukaryotic (animal and plant) cells contain their genetic material - DNA enclosed in a nucleus
Define prokaryotic cells
Prokaryotic cells are much smaller than eukaryotic cells and they do not have a nucleus, their genetic material consists of a single loop of DNA, (some prokaryotic cells- bacteria, has small rings of DNA called plasmids)
Give three additional features of prokaryotic cells
Prokaryotic cells have a cell membrane, cell wall and cytoplasm
Express 1cm as an equation
1cm = 1 x 10^-2m Meaning 1cm = 1/100th a meter
Give two additional features of eukaryotic cells
Eukaryotic cells contain a cell membrane and within the cell membrane is cytoplasm
Express 1mm as an equation
1mm = 1 x 10^-3m Meaning 1mm = 1/1000th a meter
Express 1 micrometer as an equation And draw the measurement for micrometers
1 micrometer = 1 x 10^-6m Meaning 1 micrometer = 1/1,000,000th a meter
Express 1nm as an equation
1nm = 1 x 10^-9m Meaning 1nm = 1/1,000,000,000th a meter
State a measurement using the measurement manometers
Proteins are measured using nanometers such as the haemoglobin molecule which is 5nm
When is order of magnitude used?
Order of magnitude is used when the someone wants to compare the approximate size of different objects
Define order of magnitude
Every order of magnitude is 10x greater than the one before 1 order of magnitude is 10x (1 is 10^-1) and 2 orders of magnitude is 100x (2 is 10^-2) The equation to calculate the order of magnitude N = a x 10^b Where a is an integer and N is the order of magnitude number
List the five structures of an an animals cell and describe their functions
Cytoplasm - execute chemical reactions, such as the first stage in respiration Cell membrane - control molecules that enter and leave the cell Mitochondria - execute aerobic respiration Ribosomes - execute protein synthesis (when cells make proteins) Nucleus - enclose DNA
List the three additional structures of a plant cell and describe their functions
The cytoplasm, cell membrane, mitochondria, ribosomes and nucleus have the same function in plant cells as animal cells Chloroplasts - contains chlorophyll which helps execute photosynthesis Cell wall - contains cellulose to help strengthen the cell Vacuole - filled with cell Sao which allows it to maintain the plants shape
Describe the function of sperm cells
The function of a sperm cell is to join wit an ovum (egg cell) in fertilisation and during this process the DNA of the sperm and ovum combine
Describe how sperm cells are specialised for fertilisation
Soren cells are specialised for fertilisation as they have a long tail which helps them to swim to the ovum, they are packed full of mitochondria giving them energy for swimming and sperm cells contain enzymes allowing them to digest through the outer layer of the ovum
Describe the function of a never cell
The function of a nerve cell is to send electrical impulses around the body
Describe how nerve cells are specialised for their function
Nerve cells are specialised to carry electrical impulse around the body as the axon carries impulses from one part of the body to another, the axons are covered with myelin which insulted the axon and speeds up the transmission of nerve impulses, at the end of the nerve cells are synapses which are junctions that allow impulses to pass from one nerve cell to another and the dendrites - head has a large surface area allowing never cells to easily connect
Describe the function of a muscle cell
The function of a muscle cell is to contract
Describe how muscle cells are adapted for their function
Muscle cells are adapted for contraction as they contain protein fibres which can shorten in contraction and their contain mitochondria which produces energy for muscle contraction
Describe the function of root hair cells and stater how their are specialised for their function
The function of a root hair cell is to absorb water and minerals. Root hair cells are specialised for absorption as they contain hairs which increase the roots surface area
Describe the function of xylem cells and state how they are specialised for their function
The function of xylem cells it does carry water and dissolved minerals from a plants root to its leaves through the stem. Xylem cells are specialised for their function as they have cell walls sealed with lignin which provides support for the plant, the end walls between the cells have been broken down forming a long tube, and xylem cells have no internal structure both of which factors allow for a easier flow of water/minerals
Describe the function of phloem cells and state how they are specialised for their function
The function of phloem cells is to carry dissolved sugars up and down the plant. Phloem cells are specialised for their function as their contain phloem vessel cells and sieve plates which allow dissolved sugars to move through the cell interior, and phloem cells contain mitochondria priding energy for the phloem vessel cells
List the seven components of an optical microscope
The seven components of an optical microscope are: - A stage where the microscope slide is placed - clips to hold the slide in place - a Light below the stage providing light that passes through the stages slide - above the stage are 3 objective lenses usually with magnifications of 4x, 10x and 40x - at the top of the microscope is the eyepiece used to look at the slide through - the eyepiece contains the eyepiece lens which usually has a magnification of 10x - an optical microscope contains a coarse focussing lens and a fine focussing lens
Explain how to use an optical microscope to view a prepared slide in four practical steps and two data collecting steps
1. Firstly place the slide onto the stage and use the clips to hold it in place 2. Then select the lowest-power objective lens (usually 4x) and turn the coarse focussing lens so the objective lens is almost touching the slide 3. Now look down the eyepiece and adjust the coarse focussing lens until the cell comes into focus, then turn the fine focussing lens so the cell comes into a clear-focus 4. Calculate the total magnification using the equation: Magnification (of the cell) = magnification of eyepiece lens x magnification of objective lens (Usually 10x x 4x ) = 40x 5. Lastly select a high power objective lens and adjust the fine focussing lens to bring the cells back into focus and record new results 6. After the practical you will be required to draw the cell sample with a magnification scale How to draw a magnification scale - place a ruler over the stage and measure the diameter of the field view in millimetres and present this measurement as a scale bar on your drawing and write down the magnification (eg. 100x)
State the problems of a light microscope
Light microscopes have limited magnification making it diffuser to view details in cell structures such as the nucleus They also have limited resolution so fine detail isn’t visible So electron microscopes where created to see in better magnification and resolution
What is the equation to calculate magnification
Magnification = size of image / size of real object
What features of prokaryotic and eukaryotic cells are visible and which are not visible under an optical microscope
Visible feature prokaryotic and eukaryotic cells: nucleus, cytoplasm, cell membrane Eukaryotic only - cell wall Possibly visible features of prokaryotic and eukaryotic cells include mitochondria and chloroplasts and vacuole Non visible features: ribosomes
State four key features of chromosomes
Four key features of chromosomes: - chromosomes are made of DNA and they are located in the nucleus - body cells contain two pairs of long and short chromosomes - the main body contains 23 pairs of chromosomes - chromosomes contain a large number of genes which determine many of our features
Describe the three main stages of the cell cycle by mitosis
In the first stage of the cell cycle by mitosis, the DNA replicates to form two copies of each chromosome it grows and also copies its internal structures such as mitochondria and ribosomes In the second stage of the cell cycle, mitosis takes place and one set of chromosomes are pulled to each end of the cell while the nucleus divides In the third stage of the cell cycle, the cytoplasm and cell membrane divide to form two identical cells
What are three of the functions of mitosis
Functions of mitosis The function of mitosis include it’s essential for the growth and development of multicellular organisms, such as plants and animals a second function of mitosis is it takes place when an organism repairs themselves such as a broken bone healing Mitosis also happens during asexual reproduction
Briefly describe the development of an ovum to specialised cells
Human growth begins in fertilisation after the ovum is fertilised it goes through mitosis and forms a ball of cells called an embryo. The embryo continues to undergo mitosis and then begins to form specialised cells such as nerve and muscle cells - this specialisation is known as differentiation
Give the scientific name for early-stage embryo cells and define what a stem cell is
The scientific name for early-stage embryo cells are embryonic stem cells A stem cell is an undifferentiated cell which can give rise to more cells of the same type and differentiate to form other types of cells
What three specialised cells can be found in bone marrow?
Stem cells in bone marrow differentiate to form specialised cells found in blood, including red blood cells, white blood cells and platelets
Describe the use of stem cells in the treatment of the bone marrow cancer: leukaemia
Firstly the patients existing bone marrow is destroyed using radiation then the patient receives a transplant of bone marrow from a donor. The stem cells in the bone marrow now divide to form new bone marrow. And the stem cells also differentiate and form blood cells
What are two common issues with bone marrow transplants?
Two common issues with bone marrow transplants The donor has to be compatible with the patient or the white blood cells produced by the donated bone marrow could attack the patients body There is also a risk of the patient adopting doners transmissible viruses
Describe the use of stem cells in therapeutic cloning and state the uses of therapeutic cloning
In therapeutic cloning a stem cell formed embryo is created with the patients genes The stem cells forming the embryo are transplanted into the patient without the chance of rejection of their immune system So they can differentiate to replace damaged or unstable cells therapeutic cloning is used to treat diabetes and paralysis
What is an example of the medical use of stem cells in plant cells?
An example of the medical use of stem cells in plant cells is in roots and buds. Roots and buds contain meristem tissue - a type of stem cell that can differentiate into any type of plant tissue at any point of the plants life. Meristem tissue can be used to clone crop plant that are resistant to diseases
Define diffusion
Diffusion is the random movement of a substance from a high concentration to a low concentration
What is the objective of diffusion
The objective of diffusion is to gain useful substances required to gain energy, grow and remove waste products
Define a concentration gradient
A concentration gradient is the difference in concentration between two solutions, or two different cells and a surrounding solution
Give molecules which enter and exit cells using diffusion
Molecules which use diffusion to enter cells include oxygen molecule Molecules which use diffusion to exit cells include carbon dioxide and urea
What are three factors that affect the rate of diffusin?
Three factors that affect the rate of diffusion: If the concentration gradient is higher diffusion will happen faster If the temperature is higher diffusion will happen faster because particles have more kinetic entry and are therefore moving faster If the surface area of the cell membrane is larger diffusion will happen faster
Why is an organisms surface area getting larger and therefore it’s volume decreasing an issue?
The problem with an object having a large surface area an a small volume is cells in the surface get enough oxygen with diffusion while cells inside the organism don’t revive enough oxygen with diffusion alone
How do filaments in fish hill allow for oxygen to enter the blood?
Fishes gills are covered in filaments which deoxygenated blood passes into and oxygen diffuses from the water into the blood so oxygenated blood returns to the body
Explain how to calculate the surface area to volume ratio
Firstly calculate the total surface area Then calculate the volume
Give three adaptations of filaments that increase the rate of diffusion
Three adaptations of filaments that increased the rate of diffusion Filaments increase the surface area of fish gills filaments have a thin membrane to produces a short diffusion pathway Filaments have an efficient blood supply to take oxygenated blood away which ensures the concentration gradient is always high
Define osmosis And state what partially permeable means
Osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane Partially permeable membranes allow only some molecules to pass through
State the contraction of dilute and concentrated solutios
Dilute solutions contain a high contraction of water while concentrated solutions contain a low concentration of water
What happens to an animal cell when placed in a dilute and concentrated solution?
Cytoplasm in animals cells has a low concentration of water and when animals cells are placed in water, a dilute solution, osmosis takes place: water moves from outside the cell to inside the cell which causes expansion and possible bursting While if animal cells are placed in a very concentrated solution water will move out of the cell and it will shrink
What happens to a plant cell when placed in a dilute solution? And what happens to a plant cell when placed in a concentrated solution?
When a plant cell is placed in a dilute solution such as water the water will move into the cell by osmosis and just like an animal cell it will expand, the cell walls in plant cell prevent it from bursting, instead the cell becomes turgid (swollen) When a plant cell is placed in a concentrated solution water moves out of the plant cell and the cell becomes flaccid (it shrinks)
Describe the practical which investigate the effects of osmosis on plant tissue in six steps
Firstly the potato is peeled because the skin can affect osmosis and three cylinders are cut out of it using a cork borer which ensures all the cylinders are equal in diameter Then a scalpel is used to cut the cylinders to an equal length (usually around 3cm) Next the length is mesusrrecusung a ruler and the weight is measured using a balance Now the cylinders are placed into test tubes and 10^3cm of 0.5 molar sugar solution is adde to the first test tube, 10^3cm of 0.25 molar sugar solution is added to the second test tube and distilled water is added to the third Then the potato is left overnight to let osmosis take place The potato is rolled in tissue kaisee to remove surface moisture Lastly the length and the mass of the clingers are measured again and the percentage change from the original values is calculated - equation to calculate percentage change =( change in value / original value ) x 100
What is should be drawn up after the osmosis practical
A graph should be drawn showing the percentage changes of mass/length against the con concentration of the sugar solution
What are the conclusions of the osmosis practical?
The conclusions of the osmosis practical are that the potato gains mass because water has moved in by osmosis. In concentrated solutions, the potato loses mass because water exits by osmosis. Then where the line crosses the x-axis there is no change in mass which means the concentration outside and inside the cell are the same so osmosis does not take place. Therefore this is also the approximate concentration inside the cell.
State what happens in active transport
Active transport requires energy from respiration as substances move from a more dilute solution to a more concentration solution - against the conversation gradient
Give an example of active transports in animal cells
In animal cells active transport is used to carry the sugar glucose into the cell of the cavity in the small intestine, the lumen. This is where food is digested and molecules such as the digested sugar glucose are produced. Active transport is use to carry glucose because the concentration of sugars in the lumen is lower than the concentration of sugars outside the cell therefore they are unable to diffuse into the cell. Lumen also contains many mitochondria which perform respiration, providing the energy needed for active transport
Give an example of active transport in plant cells
In plant cells active transport is used to move the ion magnesium, by root hair cells that transport magnesium from the soil to the leaves to make chlorophyll in the leaves. As the concentration of ions in the soil is lower than the contraction of ions inside the root hair cell, active transport is used to move the ions into the cell. Now the ions are transported to the xylem cells and ions move into the leaf Root hair cells contain lots of mitochondria to provide energy for active transport
What happens in photosynthesis?
Plants need light for their source of energy and to trap this light energy plants use the reaction: photosynthesis
Is photosynthesis an endothermic or exothermic reaction?
Photosynthesis takes in energy and is therefore an endothermic reaction
Where do photosynthesis take place?
Photosynthesis takes place in plants leaves which contains light absorbing chlorophyll
What is the word equation for photosynthesis
Carbon dioxide + water - light/chlorophyll - glucose + oxygen
What would happen if the light intensity of a plant is increased?
If light energy is increased a plant has more energy to carry out photosynthesis so the reaction gets faster
How can you tell when something is a limiting factor?
When something is a limiting factor every time it is increased or decreased the rate of the reaction will also increase or decrease
What are the five limiting factors in photosynthesis?
The five limiting factors in photosynthesis are light intensity, temperature, carbon dioxide concentration, chlorophyll, water availability and nutrient elements
Define a tissue
A tissue is a group of cells with a similar structure and function
Define an organ
An organ is a group of tissues that works together to perform a specific function, such as the stomach with contains muscle tissue and glandular tissue that release enzymes
Define an organ system
A organ system contains a group of organs which work together to form organisms
What are the three main nutrients in food?
The three main nutrients in food are carbohydrates, proteins and lipids
State why food molecules need to be digested and describe the process of digestion
Carbohydrates, proteins and lipids are all large molecules, and are therefore too big to be absorbed into the bloodstream so they have to be digested. During digestion large food molecules break down into small molecules by ensures and the small molecules can then be absorbed into the bloodstream
Describe the first five stages of digestion in the digestive system
Firstly, food is chewed in the mouth as enzymes in the saliva begun digesting the starch into smaller molecules Then the food passed down the oesophagus and into the stomach where enzymes begin the digestion of proteins, with the help of the stomaches hydrochloric acid The food spends several hours in the stomach and the churning action of the stomach muscle turns the food into a fluid; which increases the surface area for enzymes to digest the fluid now passes into the small intestine, at this point chemicals are related into the small intestine from the liver and the pancreas Then the pancreases release enzymes which continue the digestion of starch and protein and they start the digestion of lipids
Describe the next four stages digestion in the digestive system
In the sixth stage of digestion the liver speeds up the digestion of lipids and uses bile from the stomach to neutralise the released acid At this point the acid makes its way down the rest of the small intestine, the small intestines wall releases enzymes in continuance of the digestion of proteins and lipids Now food molecules in the small intestine produced by digestion are absorbed into the bloodstream either by diffusion or active transport The fluid travels to the large intestine where water is absorbed into the bloodstream, and finally faces are released from the body
What is the effect of a temperature increase on enzymes?
As the is temperature increased; the activity of the enzyme increased (reaction gets faster) because as the temperature increases the enzyme and substrate are moving faster causing more collision per droned between the substrate and the active site
Describe the optimum temperature of enzymes
At a certain temperature; the enzyme works at the fastest possible rate: the optimum temperature, and this point is the maximum frequency of successful collision between the substrate and the active site ( for most humans the enzymes optimum temperature is 37 degrees celcius)
What happens when the temperature of an enzyme is increased past the optimum temperature?
When the temperature is increased past the optimum temperature, the enzyme’s activity begins to rapidly decrease to zero, the enzyme stops working because at high temperatures the enzyme molecules vibrates which changes the shape of the active site, making the active site denatured so the enzyme can no longer catalyse the reaction
What is the effect of pH on enzymes?
Enzymes have an optimum pH where activity is at its maximum and when the pH is made more acidic or alkaline the activity drops to zero, and under these conditions the active site denatures Each enzyme has a specific optimum pH, an example of this would be a protease enzyme in the stomach which functions best at an acidic pH, or an enzyme which is released from the pancreas into the small intensive, such as lipase, functions best at an alkaline pH
What are the first four steps of the effects of pH on enzymes practical?
The first four steps of the practical: effect of pH on enzymes are First, place one drop of iodine solution into each well of a spotting tile Next take 3 test tubes. In the first test tube out 2cm cubed of starch solution, in the second hit 2cm cubed of amylase solution and in the third put 2cm cubed of pH 5 buffer solution (buffer solution is used to control the pH in biology) In the third step you place the test tubes in a water bath of 30 degrees Celsius and leave them for 10 minutes to allow the solution to reach the correct temperature Now combine the three solutions into one test tube and mud with a stirring rod then immediately return the test tube to the water bath and start a stopwatch
What do you do after returning the rest tube to the water bath?
After returning the test tube to the water bath, wait 30 seconds then use the stirring rod to transfer one drop of solution to a well in the spotting tile which contains iodine And the iodine should turn blue-black showing that starch is present Take a sample every 30 seconds until the iodine remains orange - which shows that starch is no longer present in the solution and the reaction is completed. Then record the time it took for the iodine to remain orange Finally repeat this reaction several times using different pH buffers for example pH 6, 7 and 8
What are the problems with the effect of pH on enzymes practice?
The problems which the effect of pH on enzymes practice are that samples are only taken every 30 seconds, so there is only an approximate time for the reaction to complete, this problem could be addressed by taking samples every 10 seconds Secondly the person carrying out the experiment is looking for the time it takes for the iodine to not go blue-black which may not always be obvious as the colour change tends to be gradual and some wells might have blue-black mixed with orange, this problem could be addressed by asking several opinions on wether the colour change has occurred for the reaction to be complete
Give two key facts about enzymes
Enzymes catalyse chemical reactions and they are large protein molecules that have an active site on their surface where the substrate attaches to
What does ‘enzyme specific’ mean/ describe lock and key theory?
‘Enzyme specific’ refers to when the substrate fits to the active site and the enzyme breaks it down into products, however when the enzyme is denatured it will not fit and can’t be broken down, therefore enzymes are specific - lock and key theory
Describe the digestion of proteins
Proteins found in the stomach, pancreas and small intestine are broken down by protease enzymes and when digested protease enzymes convert protein to individual amino acids which are then absorbed into the bloodstream When the same amino acids in proteins are absorbed into body cells; they’re joined in a different order in their chain to make human proteins
Describe the digestion of carbohydrates
Carbohydrates are broken down by carbohydrase enzymes and in the case of starch, amylase - which is found in saliva and pancreatic fluid, and simple sugars are produced when carbohydrates like starch are digested
Describe the digestion of lipids
Lipids contain glycerol molecules which are attached to three fatty acid molecules. Lipid molecules are digested using the enzyme lipase that is found in pancreatic fluid and the small intestine, which produces glycerol molecules and fatty acids
What are the three steps of a food test practice?
The three steps of a food test practice are: Take the food sample and grind it with distilled water to make a paste Now transfer the paste to a beaker and add more distilled water, stir so the chemicals in the food dissolve in the water Then filter the solution to remove suspended food particles
How is the presence of glucose (sugars) tested?
The presence of the glucose is tested by placing (2cm cubed of) the food solution into a test tube and adding 10 drops of Benedict solution to it, which is a blue colour. After this place the test tube into a beaker and half fill the beaker with hot water, now leave it for 5 minutes. If the presence of sugar is high the solution will turn brick-red, if it’s moderately present the solution will turn yellow and if the presence is low it will turn green
How is the presence of protein tested for?
Protein is tested for by placing (2cm cubed of) the food solution into a test tube, adding 2cm cubed of biuret solution which is a blue colour. If protein is present the solution will change from blue to pink/purple
How is the presence of lipids tested?
Lipids are tested for by placing (2cm cubed of) the food solution into a test tube, adding a few drops of distilled water and a few drops of ethanol, then gently shake the solution and if a white, emulsion forms: lipids are present
How is the small intestine adapted for absorbing products of digestion?
The small intestine is adapted for absorbing products of digestion because: it is 5 meters long so it provides a large surface area for the absorption of molecules produced by digestion, its covered with millions of villi which increase the surface area for absorption and the microvilli further increase the surface area. Villi also have good blood supply so the bloodstream rapidly removed the products of digestion which increase the concentration gradient, and they have a thin membrane which ensures a short diffusion path
What happens to molecules that aren’t absorbed by diffusion?
Any molecules that cant be absorbed by diffusion is absorbed by active transport
Describe the single circulatory system of a fish
Fishes have a single circulatory system, in which deoxygenated blood is pumped from the gills where it’s collected and becomes oxygenated, now the oxygenated blood is passed from the gills to the organs where the oxygen diffused out the blood into the body cells. Now the blood returns to the heart
What problems does the single circulatory system impose?
The single circulatory system of a fish is the blood loses a lot of pressure as it passed through the gills before reaching the organs therefore the blood travels to the organs slowly so it can’t deliver a lot of oxygen
Describe the double circulatory system of a human
Humans have double circulatory systems where deoxygenated blood is pumped from the heart to the lunges where it collects oxygen. Then this oxygenated blood truths to the heart that pumps it to the organs where the blood transfers it’s oxygen to the body cells
What benefits do the double circulatory system impose?
The benefits imposed by the double circulatory system are that blood can rapidly travel to the body cells providing the body cells the oxygen they need because the blood passes through the heart twice
What are the details of the structure of the heart?
The heart has four chambers: at the top is the right atrium and the left atrium, at the bottom is the right ventricle and the left ventricle The atria are separated from the ventricles by valves There are four main blood vessels entering and leaving the heart: the vena cava brings in deoxygenated blood from the body, the blood passes from the heart to the lungs in the pulmonary artery, in the lungs the blood collects oxygen and this oxygenated blood passes from the lungs to the heart in the pulmonary vein where the blood is then pumped from the heart to the body in the aorta
What pattern does blood flow take in the heart?
First the blood enters the left and right atrium, then the atria contracts do the blood is forced into the ventricles. The ventricles now contract and force blood out of the heart and valves stop the blood from flowing backwards into the atria when the ventricles contract.
Why does the left side of the heart have a thicker muscular wall?
The left side of the heart has a thicker muscular wall because the right side only pumps blood to the heart while the left side pumps blood around the entire body so it needs more force
What’s the heart rate controlled by?
The natural resting heart rate is controlled by the pacemaker, which can stop working correctly and if it does doctors can implant an artificial pacemaker - a small electrical device that correct irregularities in the heart
What’s the purpose of coronary arteries?
The purpose of coronary arteries is to provide oxygen to the heart muscle cells of the heart and this oxygen is used in respiration to provide the energy for contraction
What do artistes do?
Arteries carry a high blood pressure form the heart to the organs in the body
Describe the structure of arteries
Arteries have a very thick muscular wall so they can withstand they a very high pressure of blood. In arteries blood travels in surges every time the heart beats, which forms your pulse. Arteries are adapted to withstand the surges by having elastic fibres that stretch when the surge of blood passes through and the elastic fibres also recoil in between surges which keeps blood moving