Photosynthesis and Cellular Respiration

• Cells are small to increase the surface area to volume ratio
• A greater surface area relative to volume allows more substances like nutrients, gases, water and waste to pass through the cell membrane
• Folded membranes increase the surface area

Photosynthesis

• Plants convert energy from the sun, carbon dioxide, and water into oxygen and glucose through photosynthesis
• Glucose is the plants food
• Carbon dioxide plus water plus energy produces glucose plus oxygen

Cellular Respiration

• Organisms convert glucose and oxygen into carbon dioxide, water, and energy through cellular respiration
• The resultant energy helps the cell carry out all processes
• Glucose plus oxygen produces carbon dioxide plus water plus energy

Characteristics of Living Things (CHARGER acronym)

• Living organisms are composed of one or more cells and are highly organized structures
• Atoms make up molecules, molecules make up organelles and other cellular structures
• Cells form tissues, tissues form organs, organs work together to form organ systems

Homeostasis

• Cells need proper temperatures, pH levels, and appropriate concentrations of various chemicals to function properly
• Organisms must maintain internal conditions that don't range, despite environmental changes
• Homeostasis is the ability of an organism to maintain constant internal conditions, or achieve a "steady state"

Adaptability

• Traits that contribute to reproduction and survival in a specific environment will result in more offspring

• Over time, advantageous traits (adaptations) become more common in the population

• The change over time is termed evolution

• Adaptations help organisms survive in their ecological niches

• Adaptive traits can be structural, behavioral, or physiological

Reproduction

• Single-celled organisms reproduce by duplicating their DNA and dividing equally to form two new cells
• Multicellular organisms often produce specialized reproductive cells that will form new individuals
• Genes containing DNA are passed along to an organism's offspring during reproduction
• Genes ensure that the offspring belong to the same species and have similar characteristics, such as size and shape

Growth, Development, and Repair

• Growth is an organism's ability to increase in size and mass by increasing the number of cells
• Development is the transformation of the organism as it goes through the growth process
• Cells can grow new cells in a process called mitosis to repair after suffering injury

Energy Processing and Exchange with the Environment (Gas Exchange)

• All organisms use a source of energy for their metabolic activities
• Organisms capture energy from the sun and convert it into chemical energy in food through photosynthesis
• Other organisms use chemical energy in molecules they take in as food
• Organisms must remove waste from their bodies
• All living things need oxygen to stay alive to turn food into energy
• Animals and plants exchange gases between themselves and their surroundings to obtain oxygen
• Green plants exchange gases with their surroundings through stomata, which are holes in the under-surface of their leaves

Response to Stimuli

• All living things react to stimuli, meaning they are sensitive to changes in their surroundings
• Plants can grow toward a source of light, and their roots sense and move towards water
• Humans shiver when it is cold and withdraw their hands when touching something hot
• Tiny bacteria can move toward or away from chemicals (chemotaxis) or light (phototaxis)

Transport Across the Cell Membrane

• The cell membrane (plasma membrane) is selectively permeable, allowing some substances to enter or leave while stopping others
• It is a fluid mosaic model made up of many parts that move freely within the membrane, with phospholipids and proteins constantly sliding past each other

Passive Transport

• Passive transport does not require energy from the cell
• Diffusion is the movement of molecules from high to low concentration
• Osmosis is the diffusion of water molecules from low to high concentration across the cell membrane

Diffusion

• Diffusion is the passive movement of particles down a concentration gradient from an area of high concentration to an area of lower concentration
• Movement continues until the concentration of particles is uniform (equilibrium)
• Certain molecules (uncharged, small) can diffuse through a cell membrane, but others cannot (large, charged)

Osmosis

• Osmosis is the diffusion of water through a semi-permeable membrane from a dilute (low solute) concentration to a more concentrated (high solute) solution
• Cell membranes are completely permeable to water, and the amount of water in the environment impacts a cell's survival

Types of Solutions that Involve Water

• Hypertonic Solution: The cell is in a solution that is more concentrated than itself
• Movement of water out of the cell is greater than movement of water into the cell, causing the cells to shrink and shrivel
• Hypotonic Solution: The cell is in a solution that is less concentrated than itself
• Movement of water into the cell is greater than movement of water out of the cell, causing the cells to swell and burst
• Isotonic Solution: The cell is in a solution that has an equal concentration to itself
• Movement of water out of the cell is equal to movement of water into the cell

Active Transport

• Active transport is the transfer of a substance across a cell membrane against its concentration gradient and requires energy
• Special proteins within the cell membrane act as specific protein "carriers"
• The cell uses energy to move substances through the carrier proteins
• Different carrier proteins allow for the movement of different substances through the cell membrane