Biology F211

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Describe the features of a Prokaryotic cell
They only contain one membrane (no organelles). Surrounded by a cell wall made of Peptidoglycan. Contain smaller ribosomes- mesosomes. DNA is not surrounded by a membrane (nucleoloid) it exists as a circular chromosome/plasmids. Some have flagella.
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Describe how proteins are created for Exocytotic secretion
mRNA is created from the translation of DNA, it passes into the cytoplasm via nuclear pores. It attaches to a ribosome (RER) and this transcribes he code into the protein. The protein is folded into a 3D shape(carbohydrate is added for glycoproteins)
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Describe the passage of proteins from the rough endoplasmic reticulum.
They leave the RER in a membrane bound vesicle. These are recieved by the Golgi apparatus, where they are modified and stored. They are then shipped of in vesicles to the cell's surface, for exploration by exocytosis.
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What is Magnification? How is it Calculated?
The number of times larger an image is compared to its surroundings. magnification= image/actual
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What is resolution?
The ability to distinguish between two points that are close together (clarity). Using shortwave daylight instead of longwave artificial light will improve the resolving power of an optical microscope.
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What are the advantages of using light Microscopes?
Cheap to purchase/operate. Small and portable, unaffected by magnetic fields. The preparation of material is quick and material is rarely distorted. Living and dead material can be viewed in their natural colour.
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What are the disadvantages of light microscopes?
Magnifies obect up to x1500, resolution of 200nm and the depth of field is restricted.
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How does a transmission electron microscope work?
They use electromagnets to focus a beam of electrons which is then transmitted through the specimen. Denser parts of the specimen absorb more electrons making them look darker on the image.
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How does a Scanning electron microscope work?
It scans a beam of electrons through the specimen. This knocks off electrons from the specimen, which are gathered in the cathode ray tube to form an image. It can be 3D.
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What are the advantages of electron microscopes?
Magnifies objects over 500000x and has a resolving power of 1nm. It is possible to investigate a greater depth of field.
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What are the disadvantages of electron microscopes?
expensive to purchase/operate. They are very large and affected by magnetic field. The preparation is lengthy and requires expertise, a high vacuum is required so living things cannot be viewed and all images are black and white.
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What are the functions of cell membranes?
Keeping components inside the cell. Allowing selective passage in/out. Isolating organelles. Providing a site for chemical reactions. Cell recognition/signalling.
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Describe the structure and function of the Phospholipid bilayer.
Two layers of Phospholipids (two fatty acids, glycerol, phosphate head). The hydrophilic phosphate head faces the water, the hydrophobic tail points away from water. Function: to act as a barrier.
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Describe the role of cholesterol (C27H46O) in the plasma membrane.
Molecule fits between fatty acid tails, making the barrier more complete. It gives the membrane stability. The more cholesterol, the less permeable the membrane.
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What is the function of channel proteins?
They allow the passage of substances that cannot pass through the phospholipid bilayer.
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What is the function of Carrier proteins?
They actively move substances across the membrane requiring ATP.
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What is the function of receptor sites?
Allows hormones to bind with the cell so that a response can be carried.
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What is the function of Glycoproteins?
Peripheral proteins which act as receptors and are involved in cell recognition.
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What is the function of Glycolipids?
Act as receptors, involved in cell recognition and help cells agregate/form tissues.
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What is the function of enzymes and coenzymes?
To aid rections. The more membrane, the more enzymes. (surface area)
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What type of substances can pass through the bilayer?
Small and non-polar molecule eg. oxygen and carbon dioxide. Small, polar molecules eg. water diffuse much more slowly. Ions are unlikely to diffuse.
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What is diffusion?
The movement of molecules from region of high concentration to regions of low concentration down a concentration gradient through a partially permeable membrane.
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How does concentration gradient affect diffusion?
Diffusion rates will be higher when there is a greater difference in concentration between two regions.
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How does diffusion distance affect diffusion?
Diffusion over shorter distances occur at a greater rate than diffusion over a larger distance.
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How does surface area affect diffusion?
A greater surface area means a greater rate of diffusion, as there is more area for particles to diffuse.
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How does temperature affect diffusion?
Higher temperature = more kinetic energy = greater rate of diffusion.
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What is facilitated diffusion?
Large or charged molecules cannot move across membranes without the help of channel
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What is the role of channel proteins in facilitated diffusion?
They are pores in the membrane that are shaped to allow only one type of protein through.
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What is Osmosis?
The net movement of water molecules across a partially permeable membrane from a region of high water potential to a region of low water potential.
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What happens when too much water leaves cells?
Plant cells become plasmolysed and animal cells become crenated.
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What happens when too much water enters cells?
Plant cells become turgid and animal cells become haemolysed (burst)
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What is a hypotonic solution?
High concentration of water and low concentration of solute = loss in water
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What is an Isotonic solution?
same concentration of water and solute = no net movement
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What is a hypertonic solution?
Low concentation of water and high concentration of solute = gain in water
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What is active transport?
The movement of substances across membranes against their concentration gradient requiring the us of energy (ATP)
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Describe the role of carrier proteins in active transport.
Carrier proteins are shaped so that a specific molecule can fit into them at the membrane surface. When it fits the protein changes shape.
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What is Cytosis?
A form of active transport involving membrane bound vesicles/vacuoles. Regions of the plasma membrane become infolded (inavigation) or outfolded (evaginaion)
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What is Endocytosis?
The incorporation of substances from outside through a membrane bound vesicle/vacuole eg. Pinocytosis (liquid particles), Phagocytosis (solid particles) and receptor mediated (specific proteins according to membrane receptors)
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What is Exocytosis?
The release of substances from the inside to outside of the cell. It occurs by the fusion of a vesicle membrane and plasma membrane and vesicle contents are released.
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Why do cells use signalling molecules?
To gather information about the environment, respond to changes and to communicate with other cells.
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What is Mitosis?
When an existing parent cell divides into two new daughter cells. The cells are genetically identical to each other and the parent cell. There is no change in chromosome number. Mitosis is associated with growth, repair and asexual reproduction.
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What are the three stages of Interphase?
First gap phase: the cell grows and develop Synthesis: DNA replicates to form sister chromatids. Second gap phase: Nucleus is well defined. The chromosomes condense into chromatids, the centrosomes are repliacated.
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Describe early prophase.
The nuclear membrane disintergrates, the nucleolous disappears. The chromatin divides into supercoils and the centrosome divides into two.
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Describe Late Prophase
Chromosomes appear under a light microscope as double chromatids. Centrosomes move to opposite poles of the cell, creating a spindle.
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Describe Metaphase.
Chromosomes become aligned at the equator as homologous pairs. They attach to the spindle by their centromeres.
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Describe Anaphase.
The centromeres divide freeing the two sister chromatids from eachother. Each Chromatid is now considered to be a chromosome. The spindle fibres begin to shoten moving the once joined pairs to the poles of the cells, with equal numbers at each pole.
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Describe Telophase.
The daughter nuclei begin to form at the two poles surrounded b the nuclear envelope where the chromosomes have gathered. The nuclei reappear and the chromatin becomes uncoiled and not visible. The spindle breaks up and disappears.
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Describe Cytokinesis in Plant cells.
The cell plate forms where the equator was and new cell material is made along this line. Mitosis only occurs in meristematic tissue.
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Describe cytokinesis in animal cells.
A cleavage furrow pinches the cell in two.
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Describe budding in yeast.
The parent yeast cell swells on one side, forming a bud at the surface. The cell undergoes interphase and then mitosis. The replicated DNA, organelles and cytoplasm move to the bud. Cytokinesis occurs and the bud pinches off from the parent cell.
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What is the purpose of Meiosis?
To produce sex cells. Each cell is genetically unique and contains half the number of chromosomes (haploid). The chromosome is replicated once, but the cell undergoes two divisions.
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What is differentiation?
Changes occuring in cells of a multicellular organism so that each type of cell becomes specialized to perform a function.
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How are stem cells in the bone marrow differentiated to become erythrocytes and neutrphils?
Cells destined to become erythrocytes lose their nucleus, mitochondria golgi and RER. They are packed full of haemoglobin. Cells destined to becom Neutrophils keep theirs nuclues. Their cytoplasm appears granular due to a large number of lysosomes.
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How are meristem cells in the cambium differentiated to form Xylem and Phloem?
Xylem- cells elongate. Walls become waterproofed by lignin, killing cell contents. The ends of the cells break down. Phloem- cells elongate and their ends break down partially. Next to the tube are companion cells.
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Describe the structure of root hair cells.
They have a long hair-like projection which increases surface area of the root which increases the rate of diffusion.
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Describe the structure of Guard cells.
Thick outer/thin inner walls so that when the plant has too much water, they become turgid so the stomata opens and when there isn't enough water it closes. They are light sensitive also.
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Describe the structure of Palisade Mesophyll cells
Long and thin to maximize light absorbence, they contain a lot of chloroplasts to absorb maximum light for photosynthesis.
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Describe the structure of Sperm cells.
They have many mitochondria to provide energy. The acrosome releases enzymes onto the outside of the egg. They are small and this to aid movement, with a tail. They are haploid.
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Describe the structure of erythrocytes.
Biconcave shape provides large surface area for gas exchange. No nucleus, so more room for haemoglobin.
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Describe the structure of Neutrophils.
Flexible shape allows them to engulf pathogens. Large numbers of lysosomes- digestive enzymes.
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Describe the structure of Epithelial cells.
Joined by interlinking cell membranes and a membrane at the base.
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What is a tissue?
A collection of cells that are similar to each other and perform a common function.
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What is an organ?
A collection of tissues working together to perform a function.
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What is an organ system?
A number of organs working together to perform an overall life function.
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Why do organisms need an exchange system?
To obtain: oxygen, glucose, proteins, lipids, water, mineral ions to remover: carbon dioxide, ammonia, urea
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Describe how exchange systems maintain a diffusion gradient.
They have: an increased surface area, a thin membrane, a thin supply of molecules, and removal of molecules at the other side (for oxygen: highly vasculorised, moist surface, ventilation mechanism)
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Why do large organisms need a specialized exchange system?
Because their surface area:volume ratio becomes smaller and it needs more supplies. This means that the outer surface is not large enough to enable gases/nutrients to enter its body fast enough to keep all cells alive(travelling a further distance)
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How are the lungs adapted for exchange?
Large surface area: provides more space for molecules to pass through. barrier permeable to O2 and Co2 which is thin- reduces diffusion distance, narrow capillaries are in close contact with alveolus wall.
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How do alveoli improve efficiency for gas exchange?
Increases surface area for which oxygen and carbon dioxide can diffuse.
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How does the thin epithelium of alveoli increase efficiency for exchange?
Short diffusion distance.
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How do capillaries increase efficiency for exchange?
Short diffusion distance. Carries oxygen away, maintaining concentration gradient.
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How do the diaphragm and intercostal muscles improve efficiency?
Ventilation- supply of oxygen/removal of carbon dioxide.
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What is the function of Cartilage?
It plays a structural role, preventing the trachea and bronchi from collapsing.
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What is the function of Smooth muscle?
Allows the diameter of airway to be controlled. During exercise smooth muscle relaxes and widens meaning that there is less resistance to airflow.
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What is the function of elastic fibres?
On breathing in, the lungs inflate causing the elastic fibres to stretch. They then recoil which helps push air out.
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What is the function of goblet cells and glandular tissue?
They secrete mucus which traps tiny particles- reducing risk of infection.
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What is the function of ciliated epithelium?
They move in a synchronized pattern to waft mucus back up the throat. Mucus is then swallowed, the acidity of stomach kills bacteria.
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What is lung surfactant?
A phospholipid that coats the surface of the lungs. Without it, the water lining of the alveoli would cause the alveoli to collapse. Oxygen dissolves into the surfactant, making it easier to dissolve into cells.
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Describe the structure of the trachea.
Much of the wall consists of cartilage. The inside surface is a layer of glandular tissue, connective tissue, elastic fibres, smooth muscle and blood vessels. The inner lining is ciliated epithelium.
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Describe the structure of the Bronchi.
Much narrower than the trachea, cartilage is less regular. Contains glandular tissue, connective tissue, eleastic fibres, smooth muscle and blood vessels. Inner lining is ciliated epithelium.
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Describe the structure of Bronchioles.
Much narrower that brinchi. May contain cartilage and mostly consist of smooth muscle, elastic fibres. Cluster of alveoli at the ends.
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Describe the structre of alveoli.
They are one cell thick and highly vasculorised.
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Descibe what happens during Inspiration.
Diaphragm contracts, so it to moves down. At the same time, intercostal muscles contract causing the ribcage to move upwards/outwards. Volume of the thorax is increased, reducing pressure inside the lungs, air is forced in(pressure greater outside)
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Describe what happens during expiration.
Diaphragm relaxes and moves down, Instercostal muscles relax moving down/in. This decreases the volume of the thorax and increases pressure. Air pressure outside is less so air is forced out of the lungs.
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Describe what happens when a person breathes through a spirometer.
Breathing in takes oxygen from the chamber so it sinks. Breathing out pushes the chamber up. This movement is recorded on a data logger.
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What is tidal volume?
Volume of air move in and out of the lungs with each breath at rest.
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What is vital capacity?
The largest volume of air that always remains in the lungs.
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What is dead space?
Air in the bronchi, bronchioles and trachea.
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What is inspiratory reserve volume?
How much air can be breathed in.
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What is expiratory reserve volume?
How much air can be breathed out.
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Why do ventricles have thicker walls than atria?
Because they push blood out of the heart whereas atria pushes blood into the ventricles with gravity.
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Why does the left ventricle have thicker walls than the right ventricle?
Because the left ventricle needs to contract powerfully to pump blood all the way round the body. The right ventricle only needs to pump blood to the lungs.
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Describe what happens during Diastole.
The cardiac muscle is relaxed. Pressure in all four chambers is lower than that of the vena cava/pulmonary vein so blood flows into the chambers (a.v.valves are open)
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Describe what happens during Atrial Systole.
The right and left atria walls contract together. This small increase in pressure helps to push blood into the ventricles.
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Describe what happens during Ventricular systole?
Ventricle walls contract. The pressure in the ventricles exceeds that of the atria causing the atrioventricular valves to close. The pressure is higher in the ventricles than in the pulmonary artery/aorta causing the semi-lunar valves to open.
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Why is the heart described as myogenic?
Because it can initiate its own contraction.
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Describe the role of the sino-atrial node.
The SAN generates a wave of excitation which passes along the atrial node, causing the atria to contract at the same time. However this wave reaches a band of non-conducting collagen tissue which prevents the wave from passing to the ventricles.
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Describe the role of the atrio-ventricular node.
This is the only place that the wave can pass through. The AVN delays passing it on, to ensure that the ventricles contract after the atria.
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Describe the role of the Purkyne tissue.
The AVN passes the wave to the bundle of his and then to the Purkyne tissue which carries the wave to the ventricle walls so they contract from the bottom up.
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What does the PR interval show on an electrocardiograph?
The time taken for the wave to go from the SAN to the ventricles.
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What does the P wave show?
It correspond to the wave of depolarization in the atria (atrial systole)
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What does the QRS complex show?
Wave spreading across ventricles (ventricular systole)
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What does the T wave show?
The wave of repolarization during diastole.
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What does an elevation of the ST section indicate?
A heart attack
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What does a small and unclear P wave indicate?
Atrial fibrilaition
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What does a deep S wave indicate?
Abnormal ventricular hypertrophy (increased muscle thickness)
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Describe the structure of an artery.
It has a relatively small lumen to maintain pressure. Contains collagen (strength), elastic tissue (stretch/recoil) and smooth muscle (contracts/constricts). The endothelium can unfold when artery stretches.
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Describe the structure of a vein.
Relatively large lumen to ease bloodflow. Thinner layers of collagen, smooth muscle, elastic fibres and smooth muscle as they do not need to stretch/recoil. They contain valves to prevent backflow of blood.
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Describe the structure of a Capillary.
One single layer of endothelial cells to reduce diffusion distance. Narrow lumen ensures that red blood cells are squeezed are passed, helping them give up oxygen.
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How is tissue fluid formed?
At the arteriole end, the hydrostatic pressure is greater than outside, so fluid is forced out forming tissue fluid(pressure less at venus end). The water potential at the venus end is lower than that of the fluid, so some water re-enters capillaries
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How is lymph formed?
Excess tissue fluid passes into lymph vessels. Valves in lymph vessels stop the lymph from going backwards. Lymph move towards the main lymph vessels in the thorax then returns to the blood.
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Describe how a low pO2 in the tissues affects haemoglobin saturation.
In the tissues a lower partial oxygen and oxygen dissociates and diffuses. A small drop in partial pressure = a large drop in haemoglobin stauration.
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Why does haemoglobin not readily take up oxygen at low partial pressures?
Because the haem groups are in the centre of the molecule.
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What happens as the partial pressure rises?
The diffusion gradient of haemoglobin increases. After one oxygen molecule binds, the shape of the red blood cell changes shape which allows more oxygen molecules to diffuse.
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Why does fetal haemoglobin have a higher affinity for oxygen?
Because it must be able to pick up oxygen from an environment that makes adult haemoglobin release oxygen. Fetal haemoglobin must absorb oxygen from the fluid in the mother's blood, reducing partial pressure, which makes the mother's give up oxygen.
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How is carbon dioxide transported?
85% as hydrogencarbonate ions dissolved in plasma. 10% combines directly with haemoglobin forming Carbaminohaemoglobin. 5% diffuses in plasma.
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How does carbon dioxide displace oxygen in oxyhaemoglobin?
Most of the carbon dioxide is converted to carbonic acid by the enzyme carbonic anhydrase. This then dissociates into hydrogen ions and hydrogencarbonate ions. The H= ions displace the oxygen from oxyhaemoglobin to for haemoglobonic acid.
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What is the Bohr shift?
The displaced oxygen diffuses into respiring tissues. So a larger amount of carbon dioxide means that more oxygen will get to tissues at a lower partial pressure of oxygen.
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What is an open circulatory system?
Blood circulates through body and it enters the heart through pores, pumped by peristalsis.
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What is a closed circulatory system?
Blood stays in vessels, tissue fluid bathes cells. Blood flows faster and at a higher pressure.
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Why don't all animals have an open system?
In larger animals blood travels faster and transports oxygen and carbon dioxide. A low blood pressure means that there is a slow bloodflow which is not sufficient for large animals.
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What is a double circulatory system?
A transport system in which blood travels twice through the heart for each complete circulation of the body.
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What are the advantages of a double circulatory system?
It allows you to control blood pressure more closely and allows you to maintain blood pressure in large/complex animals.
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Describe the structure of Xylem.
There are no end walls, making an uninterrupted tube. The cells are dead, they have no cytoplasm, and the walls are made of lignin, giving support. Water moves in through small unlignified parts.
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Describe the structure of Phloem.
Living cells joined together to for sieve tubes, the have holes to allow passage. They have no nucleus and few organelles. Companion cells carry out the living functions of themselves and sieve tube elements.
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How is water taken up from the soil?
Root hair cells increase surface area. They absorb minerals by active transport using ATP. The minerals absorbed reduce the water potential of the cell cytoplasm. So water is taken up across the plasma membrane by osmosis.
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What is the Symplast pathway?
When water passes through the cell cytoplasm. They are connected by Plasmosdesmata.
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What is vacuolar pathway?
When water passes through cell vacuoles.
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What is the apoplast pathway?
Water passes through cell walls. When water in this pathway reaches the endodermis it is blocked by the Casparian strip, so it has to take the Symplast pathway. This us useful because cells can control whether substances in the water can get through.
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What is root pressure?
The action of moving minerals into the xylem by the endodermis drives water into the xylem by osmosis. This pushes water up the Xylem.
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What is transpiration pull?
Water molecules are held together by cohesion. As molecules are lost at the top,more water is pulled up. If the water column is broken, it can still be maintained via pits.
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What is capillary action?
Water is attracted to the sides of the Xylem due to adhesion. Because Xylem vessels are narrow, adhesion can pull water up the side.
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How does water move out of the leaf?
Water evaporates from the spongy mesophyll cells lining the substomatal air space, lowering the wp of these cells. Water vapour will then diffuse out of the stomata to the environment.
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What is Trranspiration?
The loss of water from the aerial parts of the plant and diffusion out of the stomata. the stomata
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How does the number of leaves affect transpiration rate?
More leaves means more surface area over which water can be lost.
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How does the number/size/position of stomata affect transpiration rate?
Mare large stomata means water vapour can be lost. If stomata is on the lower side of the leaf then less water vapour is lost.
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How does light affect transpiration rate?
Stomata will open for gaseous exchange for photosynthesis.
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How does temperature affect transpiration rate?
Higher temperature means warmer water molecules have more kinetic energy so they evaporate faster, increasing water potential gradient.
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How does humidity affect transpiration rate?
Moist air lowers the water potential gradient, so the rate is slower.
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How does wind/air movement affect Transpiration rate?
Lots of air movement blows away water molecules in the environment, increasing the water potential gradient.
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How is transpiration a side effect of gas exchange?
Because a plant needs to open its stomata to let in carbon dioxide, so it can produce glucose. This lets in water out at the same time- because of osmosis. So transpiration is a side effect of the gas exchange needed for photosynthesis.
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What are Xerophytes?
A plant adapted to living in a dry, arid habitat.
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Why do Xerophytes have smaller leaves?
To reduce surface area for water loss.
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Why do Xerophytes have a densly packed spongy mesophyll layer?
To reduce area exposed to air inside leaves.
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Why do Xerophytes have a thick waxy cuticle?
Reduces evaporation
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Why do Xerophytes have a hair layer?
Traps a layer of warm air, reducing water potential gradient.
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Why do Xerophytes have pits containing stomata and rolled leaves?
To trap air that can become saturated with water vapour, reducing water potential gradient.
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How do you investigate tanspiration using a Potometer?
1)cut shoot underwater at a slant (prevents air bubbles) 2)Insert shoot underwater 3)dry leaves and let the acclimatize, shut trap 4)record starting position of bubble 5)start stopwatch and record the distance moved by bubble per unit of time.
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What is Translocation?
The movement of assimilates from a source to sinks. It requires ATP and enzymes maintain a concentration gradient by changing the substance at the sink, meaning that there is a lower concentration at the sink.
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According to the mass flow hypothesis, what happens at the source?
Sucrose entering the sieve tube element reduces water potential inside the sieve tube, so water will enter. This increases hydrostatic pressure in the sieve tube element.
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According to the mass flow hypothesis, what happens at the sink?
The sucrose concentration inside cells is reduced due to sucrose being used. The sucrose molecules move by diffusion/active transport and water potential is increased. Water will then move into surrounding cells reducing hydrostatic pressure.
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According to the mass flow hypothesis, what happens along the phloem?
A pressure gradient from the source to the sink is created. The gradient pushes solutes along the sieve tubes to where they are needed.W
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What is the evidence for mass flow?
If a plant is supplied with radioactively labelled carbon dioxide, the carbon will appear in the phloem. Rining trees to remove phloem results in sugar collecting above the ring. The mouthparts of an apid show that is taking food from the phloem.
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What is the evidence against mass flow?
Not all solutes travel at the same rate. Sucrose is transported at the same rate, not faster to areas of low concentration. The role of sieve plates is unclear.
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How do we know that translocation uses ATP?
Companion cells have many mitochondria, it can be stopped by metabolic poison, and the rate of flow is so high that energy must be needed to drive to flow.
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How do we know that translocation uses this mechanism?
The pH of companion cells is higher than that of surrounding cells and the concentration of sucrose at the source is higher than that of the sink.
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