Biology AS F211

From specification F211 OCR

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Cell Structure

State the resolution and magnification that can be achieved by a light microscope

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Cell Structure

200nm micrometres resolution

x1500 magnification

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Cell Structure

State the resolution and magnification that can be achieved by a transmission electron microscope

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Cell Structure

0.3-0.2 nm resolution

x250000

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Cell Structure

State the resolution and magnification that can be achieved by a scanning electron microscope

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Cell Structure

5-20nm

x2500000

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Cell Structure

What is the difference between magnification and resolution?

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Cell Structure

Resolution is how detailed the image is. It is how well a microscope distinguishes between two points that are close together.

Magnification is how much bigger the image is than the specimen

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Cell Structure

What stain are used and why in light microscopy?

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Cell Structure

stains are colours of fluorescent dyes. They bind to chemicals or bind to specific cell structures

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Cell Structure

What stains are used for an electron microscope?

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Cell Structure

Metal particles or metal salts stain cell structures or chemicals in or on the cell

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Cell Structure

How do you calculate the magnification of an image?

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Cell Structure

Length of drawing / length of specimen

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Cell Structure

What is the function of the nucleus, nucleolus and nuclear envelope?

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Cell Structure

The nucleus contains the DNA

The nucleolus is a very dense chunk of DNA for making ribosomes

The nuclear envelope separates nuclear material from the cytoplasm

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Cell Structure

What is the function of rough and smooth endoplasmic reticulum?

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Cell Structure

Smooth ER is a series of membrane bound cavities that act as the intracellular transport system. It transports and makes lipids and steroids

Rough ER is a series of membrane bound cavities that act as the intracellular transport system with ribosomes.

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Cell Structure

What is the function of the golgi apparatus and ribosomes?

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Cell Structure

Ribosomes are the site of protein synthesis where the joining of amino acids in the primary structure of a protein occurs.

The golgi body is where proteins are modified by the addition of carbohydrate chains to make glycoproteins and packaged ready for exocytosis

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Cell Structure

What is the function of mitochondria, lysosomes and chloroplasts

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Cell Structure

Mitochondria are the site of aerobic respiration

Lysosomes are "suicide bags" containing digestive enzymes

Chloroplasts are the site of photosynthesis and contain the green pigment chlorophyll

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Cell Structure

What is the function of the plasma cell surface membrane, centrioles, flagella and cilia?

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Cell Structure

The plasma membrane regulates the movement of substances into and out of the cell. It also has receptor molecules on it, which allows it to respond to chemicals like hormones.

The centrioles are the attachment points for the spindle tubules during cell division

The flagella and cilia are involved in cell locomotion and transport of extra cellular things

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Cell Structure

Outline how proteins are produced and secreted (not protein synthesis)

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Cell Structure

Proteins are made in the ribosomes by the joining of amino acids. They then travel via the rough ER to the golgi where they are modified by attaching carbohydrate groups to them to form glycoproteins (e.g.mucus). They are then packaged and released in vesicles where they are excreted by exocytosis.

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Cell Structure

What is the function of the cytoskeleton?

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Cell Structure

It provides mechanical strength to cells, aiding transport within cells and enabling cell movement.

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Cell Structure

Describe the differences between prokaryotic cells and eukaryotic cells

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Cell Structure

Prokaryotes are mainly unicellular - eukaryotes are mainly multicellular

Prokaryotes have free DNA in a circular form - Eukaryotes have linear DNA contained in the nucleus called a plasmid

Prokaryotes have naked DNA (no histones) - Eukaryotes have DNA with histones

Prokaryotes have 70s Ribosomes - Eukaryotes have 80s Ribosomes

Prokaryotes have no ER - Eukaryotes have ER

Prokaryotes don't have envelope bound organelles - Eukaryotes have envelope bound organelles

Prokaryotes have a rigid cell wall with murein - Eukaryotes have cellulose cell walls and chitin cell walls

Prokaryotes have simple extracellular flagella - Eukaryotes have 9+2 arrangement of microtubules in intracellular flagella

Prokaryotes have mesosomes - Eukaryotes have mitochondria for aerobic respiration

Prokaryotes have no chloroplasts - Eukaryotes have chloroplasts

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Cell Structure

What are the differences between plant and animal cells?

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Cell Structure

Plant cells have chloroplast with chlorophyll

Plant cells have a cell wall

Plant cells have plasmadesmata

Plant cells have a sap vacuole

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Cell membranes

What kind of barrier is the plasma membrane?

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Cell Membranes

A partially permeable barrier

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Cell Membranes

What are the components of a fluid mosaic model of the cell surface membrane?

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Cell Membranes

(http://en.wikivisual.com/images/e/ee/CellMembraneDrawing.jpg)

Phospholipid bilayer, Channel proteins, Carrier Proteins, Glycoproteins, Glycolipids, Glycocalyx, Cholesterol

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Cell Membranes

What is the role of phospholipids in the cell surface membrane?

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Cell Membranes

They stop large polar molecules getting through like sugars and amino acids

The are a barrier to most water soluble molecules as they have a hydrophobic fatty acid tail

They are permeable to non polar molecules like fatty acids and vitamins

They allow small polar molecules through like water, CO2 and ethanol due to hydrophilic phosphate heads

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Cell Membranes

What is the role of cholesterol in the cell surface membrane?

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Cell Membranes

It prevents phospholipids from solidifying at low temperatures

It binds polar heads to non-polar tails of phospholipids

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Cell Membranes

What is the role of glycolipids in the cell surface membrane?

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Cell Membranes

They have branching carbohydrate side chains that are involved in cell recognition. They may act as receptor sites for chemical signals. With glycoproteins they are also involved in sticking the correct cells together in tissues.

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Cell Membranes

What is the function of proteins and glycoproteins in the cell surface membrane?

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Cell Membranes

Channel proteins and carrier proteins are involved in the selective transport of polar molecules and ions across the membrane. Some proteins act as enzymes in the microvilli lining the gut. Some proteins have very specific shapes so they act as receptor molecules for chemical signalling between cells.

Glycoproteins act as antigens as they can have many specific shapes. This enables cells to recognise other cells and behave in an organised way.

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Cells Membranes

What is the effect of changing temperature on membrane structure and permeability?

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The higher the temperature, the faster the molecules are moving so diffuse faster. The fluidity of the phospholipid bilayer increases as the phospholipids vibrate more, allowing the barrier to become more permeable

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Cell Membranes

Explain the term cell signalling

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Cell Membranes

Some cells signal from one cell to another. Others signal during processes occurring inside the cell. It allows cells to respond to the environment around them and act accordingly.

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Cell Membranes

What is the role of membrane bound receptors?

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Cell Signalling

They are the site where hormones and drugs can bind to inhibit the cell or trigger the uptake of molecules

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Cell Membranes

Explain the different types of passive transport

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Cell Membranes

Passive transport is the transport of molecules that does require energy. Diffusion is the net movement of molecules from an area of high concentration to low concentration across a partially permeable membrane. Facilitated diffusion is diffusion through channel or carrier proteins.

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Cell Membranes

Explain active transport

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Cell Membranes

Active transport is the movement of molecules or ions across a membrane against a concentration gradient requiring energy from respiration in the form of ATP. This happens in Protein pumps (companion cells) and Carrier Proteins (energy is required to change their shape).

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Cell Membranes

Explain endocytosis and exocytosis

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Cell Membranes

Endocytosis is the plasma membrane folding inwards (invaginating) to form a vesicle or sac surrounding the material to enter the cell

Phagocytosis (cell eating)

Pinocytosis (Cell drinking)

Exocytosis is the plasma membrane folding inwards to form a vesicle or sac surrounding material to leave the cell

Both require energy from respiration in the form of ATP to form and move vesicles

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Cell Membranes

Define osmosis

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Cell Membranes

Osmosis is the net movement of water molecules from an area of low water potential to an area of high water potential across a partially permeable barrier

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Cell Membranes

What is the effect of a hypotonic solution on a cell?

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Cell Membranes

The solution outside the cell has a higher water potential than the cell so water moves out of the cell by osmosis causing the cell to shrink and become crenated

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Cell Membranes

Explain the effects of a hypertonic solution on a cell

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Cell Membranes

The solution outside the cell has a lower water potential than inside the cell so water moves into the cell and it swells and bursts, becoming plasmolysed

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Cell division

What proportion of the cell cycle does mitosis occupy? What happens in the rest of the cell cycle

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Cell division

only a small percentage. The remaining percentage includes the copying and checking of genetic information

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Cell Division

What are the four main stages of mitosis?

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Cell Division

Prophase, metaphase, anaphase, telophase

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Cell Division

Describe what happens to the chromosomes, nuclear envelope and centrioles in prophase

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Cell Division

In prophase, the chromosomes condense and become visible, getting shorter and fatter. Centrioles start moving towards opposite ends of the cell, forming spindle fibres. The nuclear envelope breaks down.

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Cell Division

Describe what happens to the chromosomes and centrioles in metaphase?

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Cell Division

The chromosomes line up along the equator and become attached to the spindle fibres by their centromeres.

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Cell Division

What happens to the chromosomes and centrioles in anaphase?

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Cell Division

What happens to the chromosomes, nuclear envelope, cell membrane and centrioles in telophase?

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Cell Division

What is a homologous pair of chromosomes?

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Cell Division

Chromosomes that have the same genes at the same loci

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Cell Division

What is the purpose of mitosis - what are its roles?

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Cell Division

Mitosis is for growth, repair and asexual reproduction in plants and animals

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Cell Division

Outline the process of cell division by budding in yeast

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Cell Division

Yeast is a unicellular fungus. The new cells are formed by mitosis. By cytokinesis the new cell nips off the bud. Therefore the new cell is genetically identical to the original cell.

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Cell Division

What is the genetic makeup of cells produced by meiosis?

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Cell Division

Cells produced from meiosis are not genetically identical to the original cells as they are a result of sexual reproduction involving gametes with a haploid number of chromosomes.

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Cell Division

Define the term stem cell?

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Cell Division

Stem cells are characterized by the ability to renew themselves through mitotic cell division and differentiate into a diverse range of specialized cell types. Usually found in the bone marrow of adults or umbilical chord of babies.

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Cell Division

Define the term differentiation

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Cell Division

Differentiation is the specialisation of cells to carry out particular functions

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Cell Division

How are erythrocytes produced?

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Cell Division

Erythroblasts are the bone marrow stem cell which contain a nucleus and they begin to synthesise haemoglobin

They then form reticulocytes as the nucleus is pinched off. The continue to make haemoglobin until they eventually lose their ribosomes

They then form erythrocytes and are mature red blood cells

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Cell Division

How are neutrophils specialised?

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Cell Division

They contain small granules which are lysosomes which contain enzymes to digest bacteria.

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Cell Division

How are sieve tubes and xylem vessels derived from the cambium?

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Cell Division

The vascular cambium divides by mitosis to form narrow, elongated cells which divide by mitosis to form secondary phloem to the outside or secondary xylem to the inside. These cells then divide again to form sieve plate elements and companion cells attached to the secondary xylem

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Cell Division

Describe how erythrocytes, epithelial cells, sperm cells, palisade cells, root hair cells and guard cells are specialised

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Cell Division

Erythrocytes have no nucleus to allow more room for more haemoglobin so they can transport lots of oxygen to muscles for aerobic respiration. They have a biconcave shape to increase surface area so oxygen can diffuse out and into the cell more quickly. They are flexible so can fit through narrow capillaries. They are packed with haemoglobin to carry oxygen

Epithelial cells (squamous) - Smooth so less friction and create a short diffusion distance

(ciliated) - They have lots of mitochondria to make ATP to waft the cilia

Sperm cells have acrosomes which are specialised lysosomes to break down the egg cell membrane. They have lots of mitochondria to swim. They have a nucleus with a haploid number and microtubules which use ATP to move causing the tail to swim

Palisade cells are tall and thin for maximum volume to contain chloroplasts for photosynthesis which contain chlorophyll

Root hair cells are long to increase the surface area to absorb lots of water

Guard cells have unevenly thickened cell walls so cells bend when turgid. They have chloroplasts to provide energy for uptake of minerals and hence water

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Cell Division

Define the terms tissue, organ and organ system

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Cell Division

A tissue is a group of cells, plus any associated intercellular secretion, specialised to perform one or more particular functions

Organs are a group of tissues of two or more different types which work together to perform one or more particular functions

An organ system is a group of two or more organs of different types working together to perform a complex function or functions.

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Cell Division

What kind of cells make up lung tissue and explain their functions?

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Cell Division

Squamous and ciliated epithelium - Squamous epithelium are a single layer of flat cells lining a surface. The ciliated epithelium have moving cilia on them. They can waft mucus along.

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Cell Division

What cells make up stem tissue in plants?

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Cell Division

Xylem cells transport water around the plant and support the plant. The cells are mostly dead and hollow with no end walls and have thick walls for strength. Phloem tissue carries sugars around the plant. It's also arranged in tubes. Each cell has end walls with holes in them, so that sap can move easily through them. These end walls are called sieve plates

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Exchange and transport

Why do multicellular organisms need specialised exchange surfaces and single-celled organisms do not?

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Exchange and transport

Multicellular organisms have a long diffusion distance and are big so have a small surface area:volume ratio therefore need a transport system to reach all areas of the organisms whereas single-cell organisms have a large surface area:volume ration so do not require a transport system as their diffusion distance is only one cell thick.

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Exchange and Transport

What are the features of an efficient exchange surface?

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Exchange and Transport

A large surface area

A thin barrier for a short diffusion distance for Oxygen and CO2

A fresh supply of molecules to maintain a steep concentration gradient so diffusion is efficient

Removal of substances to maintain a steep concentration gradient so diffusion is efficient.

Alveoli - moist membrane so oxygen and CO2 can dissolve in water and diffuse across. Wall of alveoli is one cell thick for a short diffusion distance. They are surrounded by blood vessels to give a fresh supply and good removal of substances.

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Exchange and Transport

What are the features of the mammalian lung that adapt it to efficient gaseous exchange?

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Exchange and Transport

Alveoli with large round surface area for maximum diffusion of Oxygen and CO2.

Moist Alveoli so Oxygen and CO2 can dissolve and diffuse across

Rich blood supply to remove and supply molecules to maintain steep concentration gradient

Alveoli are only one cell thick to create a short diffusion distance

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Exchange and Transport

Describe the distribution of cartilage, ciliated epithelium, goblet cells, smooth muscle and elastic fibres in the trachea, bronchi, bronchioles and alveoli

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Exchange and Transport

The trachea has cartilage, ciliated epithelium with goblet cells, smooth muscle and elastic fibres and collagen.

The bronchi have cartilage, ciliated epithelium with goblet cells, smooth muscle, elastic fibres and collagen

The bronchioles have less and less cartilage. They have ciliated epithelium with goblet cells, smooth muscle, elastic fibres and collagen

The alveoli have no cartilage, no cilia, no goblet cells. They have squamous epithelium instead. They have very little smooth muscle but elastic fibres and collagen.

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Exchange and Transport

Describe the functions of cartilage, cilia, goblet cells, smooth muscle and elastic fibres

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Exchange and Transport

Cartilage is the firm connective tissue which keeps trachea, bronchi and bronchioles open

Cilia are a single layer of cells lining all tubes of the gas exchange system except alveoli. Hairs beat to move mucus to the back of the throat to be swallowed.

Goblet cells secrete mucus which traps dust and microbes

Smooth muscle relaxes to dilate bronchioles during exercise and contracts to constrict the bronchus

Elastic fibres recoil in expiration to push air out and stretch in inhalation to allow alveoli to fill will air.

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Exchange and Transport

Outline the mechanism of inhalation

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Exchange and Transport

The medulla's inspiratory centre send and impulse to the intercostal muscles and diaphragm to make them contract.

The ribcage moves upwards and outwards

In the thorax, the volume increases, decreasing the pressure, which causes air to be drawn in to the lungs.

The lungs inflate. Stretch receptors are stimulated which send impulses to the medulla to inhibit the inspiratory centre

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Exchange and Transport

Describe the process of expiration

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Exchange and Transport

The expiratory system is activated by the medulla and sends an impulse to the intercostal muscles and diaphragm to make them relax so air is expelled from the lungs and they deflate. Stretch receptors become inactive so the inspiratory centre is no longer inhibited and the cycle starts again.

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Exchange and Transport

What is the function of the pleural membrane?

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Exchange and Transport

It provides and air tight seal

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Exchange and Transport

What does tidal volume and vital capacity mean?

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Exchange and Transport

vital capacity is the maximum vol. of air that can be exchanged in a single breath

Tidal volume is the volume of air exchanged in a single breath

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Exchange and Transport

Describe how a spirometer can be used to measure vital capactiy, tidal volume, breathing rate and oxygen uptake

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Exchange and Transport

Vital Capacity - measure the distance between the highest and lowest peak on a spirometer graph

Tidal Volume - on the regular peaks, measure the distance between a peak and a trough

Breathing rate - measure the time between two consecutive troughs to get the rate of one breath

Oxygen uptake - two peaks at A and B. at A vol = 200cm at 30s

at B vol = 100cm at 50s

Uses 100cm of oxygen in 20seconds

5cm per second

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Transport in Animals

Explain the meaning of single circulatory system and double circulatory system

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Transport in Animals

A single circulatory system is when the blood passes through the heart once during a complete circulation

A double circulatory system is when the blood passes through the heart twice in a pulmonary circuit and systemic circuit

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Transport in Animals

Explain the difference between open and closed circulatory systems

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Transport in Animals

Open circulation is when the blood is free to flow around the body

Closed circulation is when the blood is transported inside blood vessels

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Animal Transport

What are the four chambers in the heart and other features?

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Transport in Animals

Left and right atrium and ventricle. Valves and septum

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Transport in Animals

Explain the differences in the thickness of the walls of the heart

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Transport in Animals

The atrium walls are thin as they only have to pump the blood to the ventricle which is a very short distance. The left ventricle has a very thick wall as it has to pump the blood to the rest of the body which is a very long distance whereas the right ventricle has a thick wall which is not as thick as the left ventricle as it has to pump the blood to the lungs which is a shorter distance than the rest of the body but greater than to the atrium.

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Transport in Animals

Describe the cardiac cycle with reference to the action of the valves in the heart

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Transport in Animals

Blood enters the atrium. The atria contract so the pressure in the atria exceeds the pressure in the ventricles. The atrioventricular valves open to allow blood to flow into the ventricles. Atrioventricular valves shut as the pressure in the ventricles exceeds the pressure in the atria to prevent the backflow of blood. The atria relaxes.

All the valves are shut in an isometric phase

The ventricle contracts and the semilunar valves open due to the pressure in the ventricles exceeding the pressure in the arteries. Blood is pumped from the ventricles into arteries. The ventricle relaxes

The semilunar valves close due to the pressure in arteries exceeding pressure in ventricle to prevent the backflow of blood.

All the valves are shut in an isometric phase.

Blood has been slowly filling atria till the atria contracts and the pressure in the atria exceeds pressure in the ventricles and the atrioventricular valves open.

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Transport in animals

How is the heart beat co-ordinated?

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Transport in Animals

The SAN creates an electrical impulse that spreads throught hte atrial wall causing a contraction. The impulse reaches the AVN. The impulse then travels down the bundle of His and spreads out into Purkyne fibres at the bottom of the ventricles. Ventricles contract from bottom forcing all the blood into the arteries. The atria and ventricles are separated by electrically insulating tissue. This causes a time delay in the contraction of the ventricles. This allows all the blood from the atria to be pushed into the ventricles.

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Transport in Animals

What is the tunica externa made of?

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Transport in Animals

collagen to withstand high pressure

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Transport in Animals

What is the Tunica Media made of?

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Transport in Animals

Collagen, Smooth muscle and Elastic fibres (elastin)

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Transport in Animals

What is the tunica intima made of?

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Transport in Animals

A single layer of endothelial cells and elastic fibres

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Transport in Animals

How is the Arteries structure related to its function?

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Transport in Animals

It has a thick wall to withstand high pressure generated by the heart. It has a narrow lumen to reduce resistance to blood and generate high pressure.

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Transport in Animals

Describe the structure and function of Veins

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Transport in Animals

They have thin walls as there is no need to withstand pressure

They have a wide lumen to minimise resistance

They are close to skeletal muscles which contract and exert pressure on veins to force blood back to the heart.

They have valves to prevent the backflow of blood

They are close to the exterior to protect arteries

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Transport in Animals

Describe the structure and function of capillaries

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Transport in Animals

They have a single thin layer of squamous endothelial cells giving a shorter distance for diffusion so diffusion is faster

They have a very narrow lumen so cells travel single file so O2 is close to respiring cells

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Transport in animals

what is the difference between blood, tissue fluid and lymph fluid?

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Transport in Animals

Tissue fluid doesn't contain any red blood cells or proteins or platelets

Lymph is the tissue fluid drained into the lymphatic system

all three have water, white blood cells, glucose, urea, CO2 and O2

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Transport in Animals

How is tissue fluid formed from plasma?

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Transport in Animals

Tissue fluid is formed when blood passes through the capillaries. The capillary walls are permeable to small solute molecules and ions, but not to the red blood cells, platelets and plasma proteins. Tissue fluid is therefore a watery liquid which resembles plasma minus its proteins. The tissue fluid is forced out of the capillaries by ultrafiltration.

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Transport in Animals

What is the role of haemoglobin?

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Transport in Animals

To transport Oxygen and Carbon Dioxide.

CO2 is converted into carbonic acid for transport or combines with the amine end of haemoglobin to form carbamino-haemoglobin

CO2 + H2O --> H2CO3 <--> H+ + HCO3- --> H+ + Hb --> HHb

carbonic anhydrase converts it to carbonic acid (H2CO3)

H+ + Hb--> HHb ( haemoglobinic acid)

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Transport in Animals

Describe the Bohr Effect and its significance

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Transport in Animals

High levels of CO2 decrease Hbs affinity for O2.

Hb is less saturated at a higher PP with high levels of CO2 so that means it releases O2 in higher PPs than normal. This means that O2 is released when needed depending on the saturation of haemoglobin with Oxygen

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Transport in Animals

What is special about foetal haemoglobin?

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Fetal haemoglobin has a high affinity for O2. This is because the haemoglobin needs to take up O2 more easily from the mother. It will release it easily as the PP in a baby is low

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Transport in Plants

(http://biology.nebrwesleyan.edu/benham/bio50/pltanatomy/images/dicotrootstele.JPG) label the xylem and phloem

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Transport in Plants

(http://sci.waikato.ac.nz/farm/images/dicot%20root%20stele_labelled_web.png)

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Transport in Plants

(http://iweb.tntech.edu/mcaprio/vascular_bundle_dicot_cs_40X_E.jpg) label the xylem and phloem

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Transport in Plants

(http://sci.waikato.ac.nz/farm/images/dicot%20stem_labelled_web.png)

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Transport in Plants

(http://www.westernhistological.com.au/Images/photoimages/dicot_leaf.jpg)

label the xylem and phloem

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Transport in Plants

(http://www.ucmp.berkeley.edu/IB181/VPL/Ana/AnaP/Ana23l.jpeg)

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Transport in Plants

What is the structure and function of xylem vessels?

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Transport in Plants

The xylem transports water and dissolved mineral ions around the plants

It is comprised xylem vessel cells lined with lignin which is dead cells so that water travels adhesively up the column. The end of the cells are broken down so the water can be pulled up in continuous columns

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Transport in Plants

What is the structure and function of sieve tube elements and companion cells?

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Transport in Plants

Seive tube elements transport sugars and amino acids in the plant. Companion cells have a dense cytoplasm, large nucleus and lots of mitochondria to make ATP for protein pumps

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Transport in Plants

Define the term transpiration

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Transport in Plants

Transpiration is the evaporation of water from the cell walls of spongey mesophyll cells and diffusion of water vapour from air spaces.

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Transport in Plants

Describe in terms of water potential and hydrostatic pressure how water moves between plant cells and out of plant cells

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Transport in Plants

The loss of water at the stomata by transpiration lowers the water potential and water moves down the water potential gradient from the top of the xylem to the stomata. Water moves up the xylem in the transpiration stream by mass flow. Water molecules are polar so are attracted to each other forming hydrogen bonds = cohesion. The unbroken thread of water molecules is called the cohesion tension theory. Water molecules are attracted to the lignin in the xylem vessel walls = adhesion Water is pulled up by capillary action. Water moves up the xylem going from an area of high hydrostatic pressure. A low hydrostatic pressure at the top of the xylem is caused by transpiration removing water from the leaves. High root pressure helps as ions are pumped into the base so there is a low water potential so water enters by osmosis so there is an increase in volume and pressure.

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Transport in Plants

What are the three routes that water travels by in a plant and describe them

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Transport in Plants

Apoplast route - Water and dissolved mineral ions pass between cells through the cell wall. Cellulose microfibrils form a loose mesh with lots of space through which water can pass. Water moves rapidly by mass flow

Symplast route - Water must cross the cell surface membrane to enter cells. Once inside the cell, water can pass to adjacent cells via plasmodesmata.

Vacular Pathway - Water passes through cells via the vacuoles of cells

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Transport in Plants

How does the Casparian ***** aid water transport?

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Transport in Plants

The casparian strip is in the endodermis and is one cell thick but made of a waxy material called sueberin in all the cell walls. This blocks off the passage of water via the apoplast route therefore water is forced to travel via the symplast route. It ensures water enters the central stele. It concentrates ions so that in dry conditions water and mineral ions don't move by mass flow out by the apoplast route

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Transport in Plants

How are xerophytes adapted to reduce water loss by transpiration?

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Transport in Plants

A waxy cuticle layer

Fewer stomata

Less Leaves

Only open stomata at night when it is cooler reduces diffusion of water vapour

Reduce the diameter of stomata

Hair around stomata to trap water vapour

Sunken stomata to make them less exposed to wind

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Transport in Plants

What is translocation?

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Transport in Plants

an energy requiring process transporting assimilates between sources and sinks

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Transport in Plants

What is a source?

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Transport in Plants

A source is the part of the plant where the assimilates enter the phloem

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Transport in Plants

What is a sink?

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Transport in Plants

A sink is where assimilates leave the phloem

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Transport in Plants

How does sucrose move in the phloem?

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Transport in Plants

Sucrose moves down a pressure gradient by mass flow requiring ATP

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Transport in Plants

How is the phloem loaded?

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Transport in Plants

H+ ions are actively pumped out of the companion cells into the surrounding cells via a protein pump in the cell surface membrane of the companion cells. This requires energy.

Outside the companion cells H+ ions combine with sucrose molecules

The H+ ions diffuse back into the companion cells through specialised proteins called cotransporter proteins. This is an example of secondary active transport.

Once inside the companion cells, the sucrose and H+ ions disassociate.

The sucrose diffuses through the plasmodesmata into the sieve tube element

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Transport in Plants

How does sucrose move up the phloem in the sieve tube elements?

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Transport in Plants

When sucrose enters the sieve tube element, it lowers the water potential of the cell. Water leaves the cell by osmosis lowering the hydrostatic pressure in this area. Water then moves back into the cell due to the pressure gradient. The solution moves to a region of lower hydrostatic pressure by mass flow

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Transport in Plants

How does the phloem get unloaded?

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Transport in Plants

When the sucrose reaches the sink it moves by facilitated diffusion through a channel protein into the sink. It is then converted into starch or glucose, maintaining a low sucrose concentration at the sink.

The removal of sucrose raises the water potential so H2O molecules diffuse into the sink by osmosis down the water potential gradient. This maintains a high hydrostatic pressure at the sink. The solution therefore keeps flowing from the source to the sink down a hydrostatic pressure gradient

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Transport in Plants

What is the evidence for the active loading of the phloem?

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Transport in Plants

There are lots of mitochondria in the companion cells

Metabolic poisons are applied causing the process to stop which means it does require ATP

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Transport in Plants

What is the evidence for the pumping of H+ ions?

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Transport in Plants

pH of companion cells is higher i.e. more H+ ions in the surrounding solution

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Transport in Plants

What is the evidence that the solution moves by mass flow down a pressure gradient?

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Transport in Plants

Aphids insert their stylet into phloem and when removed, sucrose continues to flow out so is not being sucked but moves by mass flow

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Transport in Plants

What is the evidence that sucrose is transported in the phloem?

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Transport in Plants

Aphids insert stylet to access sugar into the phloem

Ringing

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Comments

Katie

could be more detailed

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