Levels of organization

Organelle → Cell → Tissues → Organ → Organ system → Organism

Cell structure

Animal V.S. Plant cell

Importance of Cell Differentiation

• Cell differentiation is an important process by which a cell changes to become specialised

  • Specialised cells are those that have developed certain characteristics that allow them to perform particular functions. These differences are controlled by genes in the nucleus

• As a multicellular organism develops, its cells differentiate to form specialised cells

  • In an animal, most cells differentiate at an early stage of development

  • As a result, animal cells lose their ability to differentiate early in the life of the organism

  • Specific cells in various locations throughout the body of an animal retain the ability to differentiate throughout the life of the animal

    • These undifferentiated cells are called adult stem cells and they are mainly involved in replacing and repairing cells (such as blood or skin cells)

• Plants differ from animals in that many types of plant cells retain the ability to fully differentiate throughout the life of a plant, not just in the early stages of development

Example of specialized animal cells:

Example of specialized plant cells:

Biological molecule

Carbohydrates

• Carbohydrates contain the elements carbon, hydrogen and oxygen

• Carbohydrates can be small, simple sugars or more complex larger molecules

  • A monosaccharide is a simple sugar e.g. glucose (C₆H₁₂O₆) or fructose

  • A disaccharide is made when two monosaccharides join together, e.g. maltose is formed from two glucose molecules

  • A large polysaccharide is formed when lots of monosaccharides join together

    • Starch, glycogen or cellulose are all formed when lots of simple glucose molecules join together

    • Polysaccharides are insoluble and therefore useful as storage molecules

Lipids

• Most lipids in the body are made up of triglycerides

• Their basic unit is one glycerol molecule chemically bonded to three fatty acid chains

  • The fatty acids vary in size and structure

• Lipids are divided into fats (solids at room temperature) and oils (liquids at room temperature)

Proteins

• Proteins are formed from long chains of amino acids

• When amino acids are joined together a protein is formed

• Amino acids can be arranged in any order, resulting in hundreds of thousands of different proteins

  • Different proteins have different amino acid sequences resulting in them having different shapes; the shape of a protein determines its function

  • Examples of proteins include enzymes, haemoglobin, ligaments and keratin

Food tests

1. Benedict

   • for reducing sugars

   • Heat in a boiling water bath for 5 minutes

   • Take the test tube out of the water bath and observe the color

2. Iodine

   • for starch

   • Add drops of iodine solution to the food sample

3. Biuret

   • for proteins

   • Add drops of Biuret solution to the food sample

4. Ethanol

   • Mix the food sample with ethanol and shake

   • Allow time for the sample to dissolve in the ethanol

   • Strain the ethanol solution into another test tube

   • Add the ethanol solution to an equal volume of cold distilled water

   • A positive test will show a cloudy emulsion forming

Enzyme

• Enzymes are proteins that act as biological catalysts to speed up the rate of a chemical reaction without being changed or used up in the reaction

• Enzymes are necessary to all living organisms as they maintain reaction speeds of all metabolic reactions at a rate that can sustain life

  • For example, if we did not produce digestive enzymes, it would take around 2 - 3 weeks to digest one meal; with enzymes, it takes around 4 hours

  • Often the products of one reaction are the reactants for another (and so on)

• How enzymes work:

  • Step One: Enzymes and substrates randomly move about in solution

  • Step Two: When an enzyme and its complementary substrate randomly collide an enzyme-substrate complex forms, and the reaction occurs

  • Step Three: A product (or products) forms from the substrate(s) which are then released from the active site. The enzyme is unchanged and will go on to catalyse further reactions

• The optimum pH for most enzymes is 7

  • Some enzymes that are produced in acidic conditions, such as the stomach, have a lower optimum pH (pH 2)

  • Some that are produced in alkaline conditions, such as the duodenum, have a higher optimum pH (pH 8 or 9)

Movement of substances

Diffusion

Definition: The movement of molecules from a region of higher concentration to a region of lower concentration

• Molecules move down a concentration gradient 

• Passive process (doesn’t require energy)

• Note that the movement of molecules is random

• Molecules move into or out of living cells by diffusion when they cross the cell membrane

• Diffusion allows living organisms to, e.g.:

  • gain nutrients in the digestive system

  • gain oxygen in the lungs

  • remove waste products in the lungs and kidneys

Osmosis

Definition: The movement of water molecules from a region of higher water concentration (a dilute solution) to a region of lower water concentration (a concentrated solution), through a partially permeable membrane

• Osmosis is the diffusion of water

• Passive process (doesn’t require energy)

• The water is moving down its concentration gradient

• Partially permeable membranes prevent the movement of larger molecules

Active transport

Definition: The movement of particles across a cell membrane from a region of lower concentration to a region of higher concentration

• Energy is needed for active transport because particles are being moved against a concentration gradient

• Active transport across the cell membrane involves protein carrier molecules that are embedded in the cell membrane

• Examples of active transport in cells include:

  • absorption of the products of digestion into the bloodstream from the lumen of the small intestine

  • absorption of mineral ions from the soil into the root hair cells of plants

Factors that affect the movement of substances

• Surface area to volume ratio

  • bigger the surface area, the fastest the movement will happen

• Diffusion distance

  • smaller distance → faster movement of particles

• Temperature

  • The higher the temperature, the faster molecules move as they have more energy

• Concentration gradient

  • The greater the difference in concentration on either side of the membrane, the faster movement across it will occur

Nutrition

Photosynthesis

• Photosynthesis can be defined as the process by which plants manufacture carbohydrates from raw materials using energy from light

• Plants are

  • Autotrophs – they can make complex molecules (glucose) from simple molecules (carbon dioxide and water)

Factors that affect the rate of photosynthesis:

• Temperature

• Light intensity

• Carbon dioxide concentration

• Chlorophyll

  • The number of chloroplasts (as they contain the pigment chlorophyll which absorbs light energy for photosynthesis) will affect the rate of photosynthesis

Leaf structure

Mineral ions!!!

Balanced diet

• The necessary key food groups are:

  • Carbohydrates

  • Proteins

  • Lipids

  • Dietary fiber

  • Vitamins

  • Minerals (mineral ions)

  • Water

• Having an unbalanced diet can lead to malnutrition

• Malnutrition can cause a variety of different health problems in humans

• There are seven main food groups. These are:

  • Carbohydrates

    • Function: source of energy

    • Sources: bread, cereals, pasta, rice, potatoes

  • Protein

    • Function: growth and repair

    • Sources: meat, fish, eggs, pulses, nuts

  • Lipid (fats and oils)

    • Function: insulation and energy storage

    • Sources: butter, oil, nuts

  • Dietary fibre

    • Function: provides bulk (roughage) for the intestine to push food through it

    • Sources: vegetables, whole grains

  • Vitamins and minerals

    • Function: needed in small quantities to maintain health

    • Sources: fruits and vegetables, meats, dairy products

  • Water

    • Function: needed for chemical reactions to take place in the body

    • Sources: water, juice, milk, fruits and vegetables

• Examples of vitamins and minerals include: 

  • Calcium is needed for strong teeth and bones and is involved in the clotting of blood

    • A deficiency can lead to osteoporosis later in life

    • It is found in milk, cheese, and eggs

  • Vitamin D helps the body to absorb calcium and is required for strong bones and teeth

    • It can be found in oily fish and dairy products, and is also made naturally by the body in sunlight

  • Vitamin C forms an essential part of collagen protein, which makes up the skin, hair, gums, and bones

    • A deficiency can cause scurvy. It is found in citrus fruits and some green vegetables

  • Vitamin A is needed to make the pigment in the retina for vision

    • It can be found in meat, liver, dairy, leafy green vegetables like spinach, and eggs

  • Iron is needed to make haemoglobin, the pigment in red blood cells that helps to carry oxygen

    • It can be found in red meat, liver, leafy green vegetables, and spinach

• An individual will still require the same key food groups, but in different quantities depending on a number of factors such as age, height, sex, activity levels, pregnancy and breastfeeding

Human Alimentary Canal

The Stages of Food Breakdown

• Food taken into the body goes through six different stages during its passage through the alimentary canal (the gut):

  • Ingestion - the taking in of substances, e.g. food and drink, into the body through the mouth

  • Mechanical digestion - the breakdown of food into smaller pieces without chemical change to the food molecules

  • Chemical digestion - the breakdown of large, insoluble molecules into small, soluble molecules

  • Absorption - the movement of small food molecules and ions through the wall of the intestine into the blood

  • Assimilation - the movement of digested food molecules into the cells of the body where they are used, becoming part of the cells

  • Egestion - the passing out of food that has not been digested or absorbed (as faeces) through the anus

Peristalsis

• Peristalsis is a mechanism that helps moves food along the alimentary canal

• Firstly, muscles in the walls of the oesophagus create waves of contractions which force the bolus along

• Once the bolus has reached the stomach, it is churned into a less solid form, called chyme, which continues on to the small intestine

• Peristalsis is controlled by circular and longitudinal muscles

  • Circular muscles contract to reduce the diameter of the lumen of the oesophagus or small intestine

  • Longitudinal muscles contract to reduce the length of that section the oesophagus or the small intestine

• Mucus is produced to continually lubricate the food mass and reduce friction

• Dietary fiber provides the roughage required for the muscles to push against during peristalsis

Role of Digestive Enzymes

• Food is partially digested mechanically (by chewing, churning and emulsification) in order to break large pieces of food into smaller pieces of food which increases the surface area for enzymes to work on

• Digestion mainly takes place chemically, where bonds holding the large molecules together are broken to make smaller and smaller molecules

• There are three main types of digestive enzymes – carbohydrases, proteases and lipases

Carbohydrates

Proteins

Lipids

Bile

• Bile is an alkaline substance produced by cells in the liver

• Before being released into the small intestine, bile is stored in the gall bladder

• Bile contains bile salts. It is these molecules which emulsify the lipids, however you can use both terms interchangeably.

• Bile has two main roles:

  1. Neutralising the hydrochloric acid from the stomach

     • The alkaline properties of bile allow for this to occur

     • This neutralisation is essential as enzymes in the small intestine have a higher (more alkaline) optimum pH than those in the stomach

  2. Breaking apart large drops of lipids (fats) into smaller ones (and so increasing their surface area)

     • This is known as emulsification

• The more alkaline conditions and larger surface area allows lipase to chemically break down the lipid molecules into glycerol and fatty acids at a faster rate

Small intestine

Respiration

Gas exchange

Transport system

Excretion

Co-ordination and response