Cellular Energy

All cells require energy to function Methods of cellular energy: Photosynthesis Cellular respiration

Obtaining Energy Organisms can be classified according to how they get energy Autotrophs: organisms that use energy from sunlight or from chemical bonds in inorganic substances to make organic compounds Heterotrophs: animals or other organisms that must get energy from food instead of directly from sunlight or inorganic substances

Photosynthesis Most autotrophs use the process of photosynthesis for energy Photosynthesis: process of converting light energy from the sun into chemical energy to form organic compounds, primarily carbohydrates Photosynthesis can be divided into two stages: Capturing light/Light reactions Calvin cycle

Step 1: Capturing light Plants capture the light energy from the sun Chlorophyll absorbs the light energy Pigment is good at absorbing a certain wavelength of light Located in chloroplasts Light energy captured by the chlorophyll is needed to turn energy into food

Plants use the captured light to produce “food” Step 2: The Calvin Cycle Calvin cycle: a series of enzyme-assisted chemical reactions that produces a three- carbon sugar Plants use the captured light to produce “food” Water (H2O) and carbon dioxide (CO2) are needed to make the food Roots absorb water from the soil Carbon dioxide enters the plant through stomata Stomata: small openings on the underside of leaves Light energy changes the water & carbon dioxide into oxygen (O2) Stomata: small “pores” found in plants; stomata from the Greek stoma, meaning “mouth”

Photosynthesis Process

Chemical Formula for Photosynthesis

Importance of Photosynthesis Releases oxygen into the atmosphere Dead plant matter is a source of fossil fuel All organisms use energy from the sun– direct or indirect– captured during photosynthesis Factors that Affect Photosynthesis Light intensity Carbon dioxide levels Temperature

Energy is stored in organic molecules! Cellular Respiration Energy is stored in organic molecules! Cellular respiration: a complex process in which cells make adenosine triphosphate (ATP) by breaking down organic compounds ATP = universal energy storage molecule All organisms break down ATP for energy Energy is released when the chemical bonds in ATP are broken Both autotrophs & heterotrophs undergo cellular respiration Can be divided into two stages: Glycolysis Aerobic Respiration

Step 1: Glycolysis Glycolysis: the breakdown of glucose by enzymes, releasing energy and pyruvic acid Occurs in the cytoplasm Oxygen is not needed Small amount of ATP released

Step 2: Aerobic Respiration Two major stages: The Krebs cycle Electron transport chain Small molecules are broken into even smaller molecules Occurs in the mitochondria of eukaryotes Oxygen is required A lot of energy (ATP) is released Occurs in cytosol of prokaryotes

Cellular Respiration Process Cellular respiration is nearly 20 times more efficient than glycolysis alone

Cellular Respiration Chemical Formula How does it compare to the chemical formula for photosynthesis?

What if oxygen is missing? English lesson: aerobic = involving or requiring air a-, an- prefix means “without” or “not” anaerobic = without air What if oxygen is missing? Cannot complete aerobic respiration Anaerobic respiration aka fermentation Alcohol fermentation Yeast Glucose  ATP + CO2 + alcohol Make beer, wine, bread Lactic acid fermentation Bacteria, animals Glucose  ATP + lactic acid Bacteria make yogurt Animals feel muscle fatigue No oxygen or no mitochondria (bacteria) Can only make very little ATP Large animals cannot survive Lactic acid buildup in muscles = makes cells’ cytosol more acidic  reduced capacity for cell to contract, causing cramps

Turns energy into sugars Turns sugars into energy Photosynthesis Respiration Turns energy into sugars Turns sugars into energy Summary: Glucose is made during photosynthesis Glucose is broken down and energy is released during respiration All organisms use energy released to do everything