Summary: Chloroplast Photosynthesis occurs in two stages: light reactions and the Calvin cycle. Chloroplasts are organelles specific to plant cells where photosynthesis takes place... Summary: Chloroplast Photosynthesis occurs in two stages: light reactions and the Calvin cycle. Chloroplasts are organelles specific to plant cells where photosynthesis takes place. Light reactions occur in the thylakoid membranes of the chloroplast. Electron carrier molecules are arranged in electron transport chains that produce ATP and NADPH. Chloroplasts contain grana, thylakoid membranes, and stroma, which are essential for photosynthesis. Summary: Glucose and ATP Glucose is the carbohydrate produced by photosynthesis and is the near-universal food for life. ATP is the usable form of energy for cells and is referred to as the 'energy currency' of the cell. Glucose carries a packet of chemical energy just the right size for transport and uptake by cells. ATP molecules store smaller quantities of energy, releasing just the right amount to do work within a cell. Cells use about 10 million ATP molecules per second and recycle all of its ATP molecules every 20-30 seconds. Summary: Autotrophs and Heterotrophs Autotrophs store chemical energy in carbohydrates they build themselves, while heterotrophs must consume food for energy. Photosynthesis is used by autotrophs like plants, algae, and some bacteria to convert sunlight into chemical energy. Chemosynthesis is an alternative method used by some bacteria to produce food using chemical energy stored in inorganic molecules. Cellular respiration is the process of breaking down glucose to release energy and produce ATP, used by both autotrophs and heterotrophs. Photosynthesis and cellular respiration work together to recycle oxygen in Earth's atmosphere and maintain the flow of energy through living organisms. Summary: Plant Cell Structure Plant cells have unique structures like cell wall, large central vacuole, and plastids such as chloroplasts. The cell wall provides structural support and protection to plant cells. The central vacuole maintains turgor pressure against the cell wall and stores pigments. Chloroplasts are responsible for photosynthesis, converting light energy into sugars for food. Chloroplasts have a complex structure with thylakoids and grana, containing light-absorbing pigments. Summary: Cell Structure The endoplasmic reticulum (ER) is involved in lipid synthesis and protein synthesis and transport. The Golgi apparatus modifies, sorts, and packages substances for secretion or use within the cell. Vesicles are used as chemical reaction chambers and include transport vesicles, lysosomes, and peroxisomes. Vacuoles have secretory, excretory, and storage functions. Centrioles are made of short microtubules and are important in cell division. Summary: Ribosomes and Mitochondria Ribosomes are small cellular structures found in all cells and are the site of protein synthesis. Unlike organelles, ribosomes are not surrounded by a membrane. Mitochondria are called 'power plants' of the cell because they produce ATP, the cell's energy source. A mitochondrion has two phospholipid membranes, with the inner membrane having many folds called cristae. Mitochondria have their own DNA and are thought to be descended from prokaryotes according to the endosymbiotic theory. Summary: Nucleus Chromosomes are strands of DNA wrapped around proteins and contain genes that code for proteins. The nucleus has a double membrane called the nuclear envelope with pores for transport. The nucleolus is a central region in the nucleus that is responsible for building ribosomes. Nuclear pores connect the nucleus to the cytosol for molecule and information transport. Summary: Membrane Proteins Cell membrane proteins assist substances in crossing the membrane. Integral membrane proteins are permanently embedded, while peripheral proteins are temporarily associated. The Fluid Mosaic Model depicts the cell membrane's structure and fluid-like behavior. Cilia and flagella are extensions of the cell membrane. Membrane proteins can be classified as transmembrane or integral monotopic. Summary: Cytoplasm and Cytoskeleton Cytoplasm consists of everything inside the cell membrane excluding the nucleus in a eukaryotic cell. Cytoskeleton is a cellular 'skeleton' with three main fibers: microtubules, intermediate filaments, and microfilaments. Microtubules are the thickest cytoskeleton structures, made of alpha and beta tubulin filaments. Intermediate filaments organize cell structure by holding organelles and providing strength. Microfilaments are the thinnest cytoskeleton structures, made of two thin actin chains twisted around one another. Summary: Phospholipid Bilayer The cell membrane forms a barrier between the cytoplasm and the environment outside the cell. The cell membrane has selective permeability, allowing only certain substances to pass through. The cell membrane is primarily composed of phospholipids arranged in a bilayer. Hydrophobic tails of the phospholipids are on the interior of the membrane, while hydrophilic heads point outwards. Hydrophobic molecules can easily cross the cell membrane, while hydrophilic molecules need help from special proteins. Summary: Prokaryotic and Eukaryotic Cells There are two types of cells: prokaryotic and eukaryotic. Prokaryotic cells lack a nucleus, while eukaryotic cells contain a nucleus. Eukaryotic cells have organelles that perform specific functions. Prokaryotic cells are found in single-celled organisms like bacteria. Eukaryotic cells are found in multicellular organisms like animals, plants, and fungi. Summary: Parts of the Cell The term 'cell' was first used by British scientist Robert Hooke in 1665. Anton van Leeuwenhoek discovered 'animalcules', now known as bacteria. The cell theory states: all organisms are made of cells, life functions occur within cells, and cells come from preexisting cells. All cells have common parts: cell membrane, cytoplasm, ribosomes, cytoskeleton, and DNA. Cells have diverse shapes, often related to their functions. Summary: Krebs Cycle The Krebs cycle is the second stage of cellular respiration. It starts with pyruvate from glycolysis and involves a series of reactions. Energy is captured in molecules of NADH, ATP, and FADH2. Carbon dioxide is released as a waste product. Two turns of the Krebs cycle are needed for each molecule of glucose. Summary: Electron Transport Electron transport is the final stage of aerobic respiration, transferring energy from NADH and FADH2 to ATP. High-energy electrons move along electron transport chains on the inner membrane of the mitochondrion. Energy from electrons is used to pump hydrogen ions across the inner membrane, creating a chemiosmotic gradient. Hydrogen ions flow back through ATP synthase, producing ATP. A maximum of 34 ATP molecules can be produced during the electron transport stage. Summary: Neuron The nervous system is a complex network that carries electrical messages throughout the body, including the brain, spinal cord, and nerves. Nervous tissue consists of two basic types of nerve cells: neurons and glial cells. Neurons transmit electrical signals called nerve impulses. A neuron consists of three basic parts: the cell body, dendrites, and axon. The axon transmits nerve impulses to other cells. The axon of many neurons has an outer layer called a myelin sheath, which allows nerve impulses to travel rapidly. Neurons are classified based on the direction in which they carry nerve impulses: sensory neurons, motor neurons, and interneurons. Summary: Senses The five senses are hearing, sight, taste, touch, and smell, all connected to the nervous system. Each sense organ has special cells called sensory receptors that respond to a specific type of stimulus and send nerve impulses to the brain. Sight is the ability to sense light, with the eye being the organ that senses light. Light passes through various parts of the eye before reaching the retina, which sends nerve impulses to the brain. Hearing is the ability to sense sound waves, with the ear being the organ that senses sound. Sound waves enter the ear and cause vibrations that are interpreted by the brain. Taste and smell are abilities to sense chemicals, with receptors in the tongue and nose respectively. Touch is the ability to sense pressure, with pressure receptors mainly found in the skin. Summary: Glycolysis Glycolysis is the first stage of cellular respiration and does not require oxygen. It involves splitting one glucose molecule into two pyruvate molecules. Glycolysis takes place in the cytosol of the cytoplasm. The process uses 2 ATP molecules and produces 4 ATP and 2 NADH molecules. Glycolysis is considered a universal and ancient pathway for making ATP. Summary: Cellular Respiration Cellular respiration transfers energy from glucose to ATP. It has three stages: glycolysis, Krebs cycle, and electron transport. Glycolysis occurs in the cytoplasm, while Krebs cycle and electron transport occur in the mitochondria. The structure of the mitochondrion, with inner and outer membranes, plays a crucial role in aerobic respiration. Glucose is a quick source of energy as it can be readily absorbed by cells and used in cellular respiration. Summary: Photosynthesis Chloroplasts capture sunlight energy by exciting electrons in pigment molecules and splitting water molecules. Excited electrons pass through electron transport chains (ETCs), releasing energy used to pump hydrogen ions into thylakoids. A chemiosmotic gradient is formed by the concentration of hydrogen ions, which is used to produce ATP. Light re-energizes electrons, which travel down a second ETC and bond hydrogen ions to NADP+ to form NADPH. Light reactions transform light energy into chemical energy stored in NADPH and ATP, and release oxygen gas as a waste product. Read more