Chapter 1 and 2: Cells and movement of substances

• Cell membrane:

  • Controls movement in and out of cell
  • Is a partially permeable membrane
  • Made of proteins and lipids
• Cell wall:

  • Made of cellulose
  • Protects plant cells from injury
  • Fully permeable
• Cytoplasm :

  • Where cellular activities occures
  • Contains all organelles of cell
• Nucleus :

  • Controls cell activity such as growth and repair
  • Essential for cell division
  • Surrounded by nuclear membrane
• Chromosomes:

  • long thread like substance
  • Made of protein and deoxyribonucleic acid (DNA)
  • DNA carries instructions cells need for carrying out its activities
  • Chromosomes condense into thick rod-shaped structures in cell division
• Rough Endoplasmic Reticulum:

  • Ribosomes attached to surface
  • Outer surface is continuous with nuclear membrane
  • Synthesizes proteins to be transported out of cell
• Ribosomes:

  • Attached ribosomes are attached to rough endoplasmic reticulum and synthesizes proteins to be transported out of cell
  • Free ribosomes synthesize proteins to be used within the cell
• Smooth endoplasmic reticulum:

  • No ribosomes attached
  • Synthesize substances such as fats and steroids
  • Converts harmful substances to harmless ones through detoxification
• Golgi body:

  • Chemically modifies substances made by ER
  • Stores and packages modified substances in vesicles to be secreted out of cell
  • Vesicles can be seen pinching off one side of golgi body
• Secretion of substance out of cell:

  1. Vesicles containing substances produced by ER pinches off the ER
  2. Vesicles fuse with Golgi Body and release their contents to be modified
  3. Secretary vesicles containing modified substances pinches off Golgi body
  4. Secretary vesicles fuses with cell membrane and substances are releases out of cell
• Mitochondria:

  • Releases energy through aerobic respiration for cell to perform cellular activities
• Chloroplast:

  • Oval in shape
  • Contains chlorophyll
  • Is needed for photosynthesis
• Vacuoles:

  • Fluid filled spaces enclosed in partially permeable membrane
  • Stores substances within cell
  • Plant cells has large central vacuole containing amino acids, mineral salts and sugars
  • Animal cells have multiple small vacuoles that are temporary that contain water and food substances
• Red blood cell:

  • Contains haemoglobin that binds to oxygen
  • Has a biconcave shape to increase surface area to volume ratio allowing oxygen to diffuse in and out of cell at a faster rate
  • Lacks a nucleus allowing RBC to carry more haemoglobin, allowing it to bind to more oxygen
  • Is flexible, allowing it to squeeze through blood capillaries
• Muscle cells:

  • Long and cylindrical in shape
  • Contains many nuclei and mitochondria to provide the cell the energy it needs for the contraction of the cell
• Root hair cell:

  • Has long and narrow root hair to increase surface area to volume ratio allowing the cell to absorb more water and mineral salts
• Concentration gradient:

  • Difference in concentration between 2 regions
• Diffusion: Net movement of particles from region of high concentration to region of low concentration (i.e: down concentration gradient
• Diffusion across membrane:

  • A permeable membrane allows both solvents and solutes to pass through it, allowing for diffusion of these substances
• Surface area to volume ratio:

  • The greater the surface area to volume ratio, the faster the rate of diffusion
• Optimum size

  • Cell would grow to optimum size with the greatest surface area to volume ratio and stop growing
• Adaptations that increase surface area to volume ratio:

  • Having protrusions
  • Having folds in the cell membrane
• Osmosis: Diffusion of water molecules through partially permeable membrane
• Water potential:

  • Tendency of water molecules to move from one place to another
  • The more water molecules presents, the more water potential it has
• Plant cell in solution with high water potential:

  1. Cell sap has lower water potential than solution
  2. Water molecules enter cell through the partially permeable cell membrane by osmosis
  3. Cell expands and swells, becoming turgid
  4. As water molecules enter the cell, the vacuole increases in size and pushes the cytoplasm against the cell wall, the cell does not burst as its protected by the cell wall
• Turgor: Turgidity of cell with water
• Turgor pressure: Pressure exerted by water in vacuole
• Animal cell in solution with high water potential:

  1. The cytoplasm has lower water potential than the solution
  2. Water enters cell through partially permeable cell membrane
  3. Cell expands and burst since it does not have a cell wall to protect it
• Plasmolysis (plant cell):

  1. Plant cell in solution with low water potential, cell sap has higher water potential than solution
  2. Water molecules from vacuole and cytoplasm leaves the cell through the partially permeable cell membrane through osmosis
  3. Cell becomes flaccid and limp
  4. Vacuole and cytoplasm of the cell decrease in size as the cell loses water.
  5. The cytoplasm shrinks away from cell wall and the cell is plasmolyzed
  6. Cell can be restored if placed in solution of high water potential
• Crenation (animal cell):

  1. Animal cell placed in solution of low water potential, cytoplasm has higher water potential
  2. Water molecules leave cytoplasm through the partially permeable cell membrane by osmosis
  3. Cell shrinks and spikes appear on cell
  4. Cell will dehydrate and would eventually die
• Importance of Turgor in plants:

  • Allows stem of plants to remain firm and upright
  • Turgor in guard cells allows opening and closing of stomata
• Active transport: Energy is used to move the particles of a substance across a membrane against its concentration gradient
• Occurrences of active transport:

  • Uptake of glucose by microvilli of epithelial cell in small intestine
  • Root hair cell takes in mineral salt by either diffusion or active transport dependent on the concentration of mineral salts