Biology Unit 1


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Observing Cell Structure

Magnification - The degree to which the size of an image is larger than the object itself.

Resolution - The degree to which it is possiable to distinguish the difference between two objects that are close together.

Actual Size = Image Size/ Magnification

Electron Microscopes

Transmission Electron Microscope (TEM) - An electron beam passes through a thin prepared sample, final image is 2D, magnification possiable is x500,000

Scanning Electron Microscope (SEM) - An electron beam is directed onto the sample, final image is 3D of the surface, magnification possiable is x100,000

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Cell Structure and Function

Eukaryotic cells - Have a true nucleus and membrane - bound organelles

Prokaryotes - Have naked DNA and small organelles with no membrane - bound organelles.


Nucleus - contains DNA, forms chromosomes

Mitochondria - 2 membranes, inner is folded to form cristae, formation of ATP

Golgi Apparatus - Flattened continous membrane with ER, processes molecules and transports them

Endoplasmic Reticulum (ER) - Membrane bound sacs which forms sheets called cisterine, rough ER contains ribosomes collects protiens manufactured by ribosomes, smooth ER is involved in manufacruring lipis and seroids

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Cell Structure and Function Continued

Ribosomes - Very small made of RNA, manufacture protien and they are attached to the rough ER

Lysosomes - Spherical sacs of enzymes, breack down unwanted cellular components

Centrioles - Hollow cylinders that form microtubes, centrioles are important in cell division



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Cell Membrane

Active Processes

Active transport - Against a concentration gradient via carrier proteins that use energy from ATP in order to change shape.

Endocytosis and Exocytosis - Bulk transport of materials via vesicles that can fuse with or break from the cell surface membrane.


Passive Processes


Diffusion - Down a concentration gradient lipid soluble or very small molecules throught lipid bilayer and osmosis.

Facilitated Diffusion - Down a concentration gradient charged or hydrophilic molecules or ions via channel or carrier protiens.

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Passive Processes

Diffusion - A passive molecules diffuse down gradient with no energy needed, they have their own kinetic energy.

The rate is affected by - Temperature, concentration gradients, stirring/moving, surface area distane/thickness, size of molecule

Channel Proteins - Are like pores, only allow one type of ion through sometimes are gated. Ions like Na ions and Ca ions

Carrier Proteins - Shaped for specific molecule, protien changes shape to allow mollecule through eg. Glucose and amino acids.

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Water Potential/ Osmosis


Osmosis - is a special kind of diffusion, it is only the movement of water molecules by diffusion and across a partially permeable membrane.

Water potential - A measure of the concentation of water molecules that are able to diffuse. Pure water has the highest amount of free molecules 0kPA (kiloPascals). Lower water potential is -10kPA.

In Pure Water - Animal cells take in water from osmosis until they burst open haemolysed, plant cells have a cell wall which prevents bursting. Membrane pushes against the wall to becomeTurgid.

In Concentrated solution - Animal cell loses water through osmosis and shrinks and appears wrinkled crenated, plant cell loses water through osmosis and plant cell membrane pulls away from cell wall as water leaves plasmolysed

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Mitosis - it is involved with Growth .e.g. cells in an eymbryo divide to form tissue stem cells Replacement of Bome marrow to Red blood cells and neutrophils. Repair, e.g. in wound healing. Asexual reproduction

Interphase - DNA replicates in this stage.

Mitosis - the nucleus divides and chromatids separate.

Cytokinesis - the cytoplasm divides or cleaves.

Growth phase - each new cell grows to full size.

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Mitosis Continued

Mitosis in 4 stages

Prophase - replicated chromosomes supercoil (shorten and thicken),each chromosome is now two chromatids.Nuclear envelope breaks down. Centrioles move to opposite poles of the cell.

Metaphase- Chromatids come to the middle of the cell. Centrioles organise microtubules into the spindle which attach to centromes.

Anaphase - Chromatids break apart at the centromere and are pulled by the spindle towards poles. Once separated they become chromosomes. 

Telophase - Nuclear envelopes re-form around each group of chromosomes at each end of the cell. The chromosomes uncoil.

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Organising the Organism

Tissues - A collection of cells that are similar to each other and perform a common function. They may be found attached to each other, but not always. eg. xylem and phloem in plants.

Organs - A collection of tissues working together to perform a particular function is called an organ. eg. leaves in plants and the liver in animals.

Organ systems - An organ system is made up of a number of organs working together to perform an overall life function. eg. excretory system and the reproductive system.

Plant tissues - Xylem and phloem come from diving meristem cells such as cambium, meristem cells undergo differentation to form the different kinds of cells in the transport tissues, xylem transports water and ions, phloem transports sugars (mainly sucrose) and other compounds made by plants.

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Animal Cells

Squamous epithelial tissue - Made of flattened cells, thin, smooth, flat surface. Ideal for lining inside of tube ie. blood vessels, Where fluids can pass easily over them, are held in place by the basement membrane, it is made out of collagen and glycoprotiens.

Ciliated epithelial tissue - Made up of column-shaped cells, found on the inner surface of the tubes eg. trachea, bronchi and bronchioles, "exposed" surface covered with tiny projections called cilia, which wave in rhythm and move stuff like mucus.



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Gaseous Exchange


The alveolus wall is an efficient exchange surface as it is only one cell thick a squamous cell. It is moist and is highly folded for a large surface area, Alveoli are supplied with a rich network of capillaries which carry blood closeto the alveolus wall

Intercostal muscles on the ribs - Contract to raise the ribs, relax which makes the ribs fall

Muscle fibres in alveolus wall contract/relax to move air in and out of the lungs ventilation. Along with the blood supply, this keeps up a concentration gradient of oxygen and carbon dioxide.

These features increase the rate of diffusionof oxygen into the blood from the alveolus and carbon dioxide out of the blood into the alveolus.

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Inspiration - Pressure in chest cavity drops blow atmospheric pressure

Expiration - Pressure in lung increases and rises above atmospheric pressure.

The trachea and bronchi have rings of cartilage which keep them open for airflow during ventilation.

Smooth muscle contracts and narrows the bronchi and bronchioles and elastic tissue opens these airways. This controls airflow.

Goblet cells in the lining of the trachea, bronchi and bronchioles secrete mucus which traps particles (e.g. pollen and bacteria).

Ciliated epithelial cells in the lining beat upwards. This removes any swallowed mucus or particles, keeping the lungs clean.

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Transport Systems

Large multicellular animals have a small surface area for their volume, resulting in a large distance for diffusion of gases.

Single system - fish, heart - gills - body - heart.

Double system - mammels, Left heart - body - right heart - lungs - left heart.

Cosed circulatory system - fish, birds and mammals, blood stays in blood vessels.

Open system - insects, blood leaves vessels.

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The left ventricle wall (thick/high pressure) pumps blood around the body. The right ventricle wall (thinner/low pressure) only have to pump blood to the lungs.

Atrial wall are very thin since they only have to pump blood a short distance into the ventricles.

Cardiac cycle - Chambers fill diastole ventricles contract ventricular systole Atrio-ventricular valves close, "lub" sound; atria contract atrial systole semi-lunar valves close, "dub" sound.

The Sino-artial node (in right atrium) maintains beat rhythm. The AtrioVentricular Node and Purkyne fibres pass the beat on to ventricles.

Coronary Atrteries lie over the surface of the heart. They carry oxygenated blood to the heart itself.

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Heart Continued

Veins carry blood to the heart.

Arteries carry blood away from the heart.

String-like tendinous cords attach valves to the walls of the venricles and prevent the flimsy valves turning inside out.

P- shows the excitation of atria. QRS- indicates the excitation of ventricles. T- shows diastole.


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Blood contains cells, plasma proteins and dissolved substances.

Tissue fluid is blood minus cells and plasma protiens.

Harmoglobin Hb in red blood cells erythrocytes picks up oxygen easily at the lungs where oxygen pressure is high Hb dissociation curve is to the left and S-shaped and releases it at tissues where oxygen pressure low, down a diffusion gradient

Carbon dioxide from tissues combines with Hb, making it release oxygen Carbon dioxide makes the dissociation curve move to the right This Bohr effect means more oxygen for active tissues. The carbon dioxide diffuses into plasma.

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Blood Continued

Arteriescarries blood away from the heart, small lumen to maintain high pressure, wall is relatively thick contains collagon, a fibrous protien to give it strength to withstand high pressure, contains elastic tissue thats allows wall to stretch and recoil. The recoil maintains the high pressure while heart is relaxed, contains smooth muscle which contract to reduce blood flow to certain organs, folded endothelium so can unfold when the artery is stretched.

Veins - large lumen to ease the flow of blood, thinner layers of collagon, smooth muscle and elastic tissue. They do not need to stretch and recoil and do not contrict blood flow, main feature valves that prevent blood flowing in the wrong direction.

Capillaries - has very thin walls. This allows exchange of materials between the blood and cells of tissue via the tissue fluid, lumen is very narrow. Red blood cells are squeezed this helps them gve up oxygen.

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Roshni Rabheru


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