Biology🌱🦠🧪

• Many organs are part of more than one organ system
• Most eukaryotic cells have the same internal organelles, but cell specialisation means cells often differ in number and have more room for transporting oxygen
• Groups of cells that carry out a common function are known as a tissue, groups of tissues that work together to carry out a common function form an organ and groups of organs that carry out a common function form an organ system
• Types of cells

  • Eukaryotic
  • Prokaryotic
• Eukaryotic cells

  Contain a nucleus and membrane-bound organelles
• Ultrastructure of eukaryotic cells

  1. Nucleus is surrounded by a double membrane called the envelope containing pores which enable molecules to enter and leave the nucleus. The nucleus also contains chromatin and a nucleolus which is the site of ribosome production

  2. Rough endoplasmic reticulum (RER) is a series of flattened sacs enclosed by a membrane with ribosomes on the surface. RER folds and processes proteins made on the ribosomes

  3. Smooth endoplasmic reticulum (SER) is a system of membrane-bound sacs. SER produces and processes lipids
• All living organisms are made of cells
• Bacteria cells are prokaryotic whereas human cells are eukaryotic
• Obtaining a more detailed structure of cells

  Using a microscope to view the ultrastructure
• Prokaryotic cells

  Don't contain a nucleus and membrane-bound organelles
• Carbohydrates

  Molecules consisting of carbon, hydrogen, and oxygen, forming long chains of sugar units called saccharides
• Monosaccharides

  • Monomers of carbohydrates
  • Soluble in water and small, simple molecules
• Formation of disaccharides

  2 monosaccharides join together in a condensation reaction to form a disaccharide
• Polysaccharides

  • Glycogen
  • Starch
• Starch

  • Primary energy store in plants, mixture of amylose and amylopectin, amylose is unbranched and compact, amylopectin is branched and rapidly digested
• Polysaccharides

  • Formed from many monosaccharides of glucose joined together, used as energy stores
  • Large molecules with a compact shape, easily hydrolysed to release energy, insoluble with no osmotic effect in cells
• Joining monosaccharides to form disaccharides and polysaccharides

  Monosaccharides can join through condensation reactions to form glycosidic bonds, broken apart by hydrolysis reactions
• Types of saccharides

  • Monosaccharides
  • Disaccharides
  • Polysaccharides
• Water

  • Hydrogen atoms are more positive than the oxygen atom, causing one end of the molecule to be more positive than the other
  • Water has a permanent dipole, making it a polar molecule
  • Substances can dissolve in water due to positive and negative charges within the molecule
  • Dissolved substances can move, allowing chemical reactions to occur
• Glycogen

  • Main energy storage molecule in animals, formed from many glucose molecules joined together by 1,4 and 1,6 glycosidic bonds, has side branches for quick energy release
• Types of lipids

  • Saturated lipids (such as those found in animal fats)
  • Unsaturated lipids (found in plants)
• The heart is comprised of 4 chambers: the left and right atria and the left and right ventricles
• Diffusion in single-celled organisms can occur directly between the external environment and the cell, known as simple diffusion
• Functions of lipids within an organism

  • Energy storage
  • Organ protection
  • Thermal insulation
  • Making cell membranes
• Circulatory system

  • Comprised of the heart and three types of blood vessels: arteries, veins, and capillaries
• Capillaries

  • Branch from arterioles to supply cells with substances from the blood
  • Numerous and highly branched with a large surface area
  • Walls are one cell thick to allow quick diffusion
  • Very narrow diameter to reach close to every cell
• Mass transport systems are needed in larger organisms to supply all cells with vital substances
• Triglycerides

  • They are made of one molecule of glycerol and three fatty acids joined by ester bonds formed in condensation reactions
  • Used as long term energy reserves in plant and animal cells
• Breaking apart polysaccharides

  Glycosidic bonds have to be broken through a hydrolysis reaction where a water molecule is added, splitting a polysaccharide into 2 smaller molecules, or a disaccharide into 2 monosaccharides
• Lipids

  • They are non-polar molecules, insoluble in water but soluble in organic solvents
  • They can be saturated or unsaturated
• Arteries

  • Take oxygenated blood away from the heart
  • Have thick walls containing muscles and elastic that expand and recoil with each heartbeat
  • Relatively small lumen
  • Contain no valves
  • Inner lining is folded to allow it to stretch
  • Split into arterioles which split into capillaries
  • Lined with smooth endothelium to reduce friction and ease flow of blood
• The atrioventricular valves prevent blood flowing back
• Veins

  • Capillaries join back up to form veins, carrying deoxygenated blood back to the heart
  • Carry blood at low pressure with thin walls
  • Have a wide lumen to maximise blood flow to the heart
  • Have valves to prevent backflow
• The semilunar valves prevent backflow of blood from the arteries into the ventricles
• The affinity of oxygen for haemoglobin varies depending on the partial pressure of oxygen
• Chambers of the heart

  • Left atria
  • Right atria
  • Left ventricles
  • Right ventricles
• The ventricles pump blood out of the heart via the arteries to the lungs or the body
• During respiration, oxygen is used up, decreasing the partial pressure and the affinity of oxygen for haemoglobin, resulting in oxygen release in respiring tissues
• Each molecule of haemoglobin can carry 4 oxygen molecules
• Deoxygenated blood returns to the lungs where carbon dioxide unloads from haemoglobin, which binds to oxygen again