Cells and Organisation

Light Microscopes can magnify up to 2,000x and have a resolving power of 200nm

Electron Microscopes can magnify up to 2,000,000 times and have a resolving power of 0.2nm

Size of image = magnification x size of real object

Animal cells contain mitochondria, ribosomes, a nucleus, cytoplasm and a cell membrane

Plant cells contain all aforementioned as well as a cell wall, chloroplasts and a permanent vacuole

Prokaryotic cells contain free genetic material, flagella, plasmids, a cell membrane, cell wall and slime capsule.

All bacteria are procaryotes.

As an organism develops, stem cells become specialised to certain functions.

Nerve cells contain lots of dendrites for connections and lots of mitochondria in the synapses to produce enough energy for the transmitter chemicals needed.

Muscle cells contain sliding proteins and many mitochondria for ATP production.

Sperm cells have a long tail for movement, an acrosome with enzymes to break down the egg cell and many mitochondria in its middle section for energy.

Root hair cells have a high surface area to volume ratio and many mitochondria for active transport, as well as a large permanent vacuole to increase osmosis.

Photosynthetic cells contain lots of chloroplasts for photosyntheses and a large permanent vacuole for rigidity of the cell.

Xylem contain lignin spirals to help it withstand the pressure of transporting water.

Phloem contain sieve plates for carrying dissolved food.

Diffusion is the movement of particles from an area of low concentration to high concentration in a gas or liquid.

Rate of diffusion is affected by difference in concentrations, available surface area and temperature.

Osmosis is the movement of water down a concentration gradient through a partially permeable membrane.

Same concentration both outside and inside = isotonic

Higher concentration outside = hypertonic || Lower concentration outside = hypotonic

Osmosis allows animal cells to maintain a healthy concentration, but can cause problems if the outside concentration changes dramatically.

Osmosis is important to maintain turgor in plant cells.

Active transport moves substances from a low concentration to a high concentration, against the concentration gradient.

Active transport requires energy produced via respiration.

It allows for root hair cells to absorb mineral ions from the soil, and also allows glucose to move from low concentration in the gut to high concentration in the blood stream.

Single cellular organisms have a relatively large surface area to volume ratio, so all necessary exchanges take place over this surface.

Multicellular organisms often have specialised exchange surfaces, which normally are adapted to have a large surface area and thin walls to ensure short diffusion distances.

They also have an efficient blood supply and are well ventilated.

Chromosomes are found in pairs. Body cells divide in a series of stages called the cell cycle.

During this cycle, genetic material is doubled, and then divides into two identical nuclei in a process called mitosis.

Before a cell can divide it need to grow, replicate the DNA to form two copies of each chromosome and increase the number of sub-cellular structures.

In mitosis, the sets of chromosomes are pulled to opposite ends of the cell, and the nucleus divides.

Finally, the cytoplasm and membrane divide into two seperate cells. Mitotic division is important in the growth, development and repair of multicellular organisms.

In plant cells, mitosis takes place in the meristems found in the shoot and the root tip.

Many types of plant cells retain the ability to differenciate throughout their life.

Most types of plant cell differenciate in an early stage of development.

Embryonic stem cells and adult stem cells can be cloned to differentiate into many types of cell.

Treatment with stem cells may be able to help with conditions such as paralysis and diabetes.

Stem cells from meristems are used to produce new plant clones quickly and economically for research, agriculture and horticulture.

In therapeutic cloning, an embryo is produced with the same genes as the patient so the stem cells are not rejected and may be used for medical treatment.

The use of stem cells has some potential risks some people have ethical or religeous objections.

A tissue is a group of similar cells all specialised to carry out the same function.

Organs are a collection of tissues working together for a specific function.

Organs are organised into organ systems, which work together to form an organisms.

The digestive system in a mammal is an organ system that works together to digest and absorb food.

Glands such as the pancreas and the salivary glands produce enzymes to break down food.

Enzymes in your mouth stomach and break down large insoluble molecules into smaller soluble molecules for absorbtion.

The gullet transports food from your mouth to your stomach, and your intestines transport digested food from your stomach to your anus, absorbing useful nutrients along the way.

The liver produces bile which aids in the digestion of lipids.

Carbohydrates are made up of units of sugar. Simple sugars are carbohydrates that only contain one or two sugar units. They turn blue benedict's solution brick red on heating.

Complex carbohydrates contain long chains of simple sugar units bonded together. Starch turns yellow-red iodine solution blue-black.

Lipids contain three molecules of fatty acids bonded to a molecule of glycerol. Ethanol added to solution gives a cloudy white layer.

Protein molecules are made up of long chains of amino acids. Biuret reagent turns from blue to purple in the presence of proteins.

Catalysts increase the rate of a chemical reaction without chemically changing themselves.

Enzymes are biological catalysts that use the lock and key theory of enzyme action.

Enzymes are proteins, with the active site being a folded amino acid chain. The substrate binds to the active site and the reaction is catalysed. Metabolism is the sum of all the reactions in a cell or body.

Enzyme activity is affected by temperature and pH, both of which can denature the enzyme in high amounts.

Digestion involves the breakdown of large insoluble molecules into soluble substances that can be absorbed into the blood across the wall of the small intestine.

Digestive enzymes are produced by specialised cells in glands.

Carbohydrases such as amylase catalyse the breakdown of carbohydrates to simple sugars.

Proteases catalyse the breakdown of proteins into amino acids.

Lipases catalyse the breakdown of lipids to fatty acids and glycerol

The protease enzymes work best in acidic conditions, which is why the stomach produces hydrochloric acid to maintain a low pH.

Enzymes in the pancreas and small intestine work best in alkaline conditions. Bile produced by the liver and gall bladder neutralise acid and emulsifies fats.

The blood, blood vessels and heart make up the human circulatory system which transports substances to and from the body cells.

Plasma has blood cells suspended in it and transports proteins and other chemicals around the body.

Red blood cells contain haemoglobin that binds oxygen to transport it from the lungs to the tissues.

White blood cells help protect the body against infection, and platelets are cell fragments that clot wounds.

The blood flows around the body in the blood vessels. The main types of blood vessels are arteries, veins and capillaries.

Substances diffuse in and out of the blood in capillaries, as they are only normally one cell thick.

The valves prevent backflow, ensuring the blood flows in the right direction.

Human beings have a double circulatory system.

Deoxygenated Blood is found in the right ventricle. This moves up the pulmonary artery to the lungs to be oxygenated.

The pulmonary vein brings the oxygenated blood from the lungs into the left atrium.

The aorta carries oxygenated blood around the body. The vena cava brings deoxygenated blood back into the heart and into the right atrium to restart the process.

Stents can be used to keep narrowed or blocked arteries open. Statins reduce cholesterol levels in the blood redicing the rist of coronary heart desease.

Damaged heart valves can be replaced using biological or mechanical valves.

Heart rate is controlled by a group of cells in the right atrium that form a natural pacemaker. These can be replaced by an electrical pace maker to correct irregularities.

Artificial hearts are occasionally used to keep patients alive while they wait for a transplant or for their heart to rest as an aid to recovery.

When you inhale, oxygen rich air moves into your lungs. This maintains a steep concentration gradient with the blood resulting in gas exchange via diffusion.

The lungs are protected by yur ribcage and seperate from your abdomen by the diaphragm.

The alveoli have a very large surface area, which allow oxygen to diffuse into the blood stream and carbon dioxide to diffuse out of the blood to be exhaled.

Plant tissues are collections of cells specialised to carry out specific functions.

The structure of the tissues in plant organs is related to their functions. The roots, stem, and leaves form a plant organ system for the transport of substances around the plant.

Xylem tissue transports water and mineral ions from the roots to the stems and leaves.

Phloem tissue transports dissolved sugars from the leaves to the rest of the plant, including the growing regions and storage organs.

The loss of water vapour from the surface of a plant is called transpiration. Water is lost through the stomata which open to let in carbon dioxide for photosynthesis.

The somata and guard cells control gas exchange and water loss.

Factors that increase the rate of transpiration are temperature, humidity, air flow and light density.

Transpiration is more rapid in hot, dry, windy or bright conditions.