https://www.khanacademy.org/science/ms-biology/x0c5bb03129646fd6:cells-and-organisms/x0c5bb03129646fd6:cells-organisms/v/ms-cells-and-organisms 2022-09-10T03:04:58.582913383Z Cells and organisms All living things are made up of cells, which is the smallest unit that can be said to be alive. An organism may consist of one single cell (unicellular) or many different numbers and types of cells (multicellular). Khan Academy video https://cdn.kastatic.org/ka_thumbnails_cache/4c87c6c9-4669-4319-91b7-935603e64401_1280_720_base.png Cells and organisms All living things are made up of cells, which is the smallest unit that can be said to be alive. An organism may consist of one single cell (unicellular) or many different numbers and types of cells (multicellular). https://cdn.kastatic.org/ka-youtube-converted/Uiqro5TUyLA.mp4/Uiqro5TUyLA.mp4 237 Observation and identification of cells (plant and animal) using microscopy and photomicrographs https://www.khanacademy.org/science/biology/structure-of-a-cell/cytoskeleton-junctions-and-extracellular-structures/v/overview-of-animal-and-plant-cells 2023-09-14T11:07:34.466749579Z Overview of animal and plant cells Animal and plant cells share common elements like plasma membranes, cytoskeletons, and mitochondria. However, they differ in certain aspects. For example, plant cells have a cell wall and a central vacuole, while animal cells contain centrosomes. The understanding of these cellular structures continues to evolve through ongoing research. Sal Khan video https://cdn.kastatic.org/googleusercontent/Dh9U2y3gOBCqEcO6KDSA71WvDYk_M0h8RMeLhY_JkocdVEkA5NRNcJwYO9m1MyaAoYiLJh3n98UfMHvyAM00zJ0 Overview of animal and plant cells Animal and plant cells share common elements like plasma membranes, cytoskeletons, and mitochondria. However, they differ in certain aspects. For example, plant cells have a cell wall and a central vacuole, while animal cells contain centrosomes. The understanding of these cellular structures continues to evolve through ongoing research. https://cdn.kastatic.org/ka-youtube-converted/24YMQ9GvLss.mp4/24YMQ9GvLss.mp4 522 Observation and identification of cells (plant and animal) using microscopy and photomicrographs https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/cell-structures-and-their-functions/v/mitochondria-video 2022-11-16T04:22:43.7414897Z Mitochondria Mitochondria are organelles that contain their own DNA, and have both inner and outer membranes. Mitochondria are often referred to as the "powerhouses of the cell" because they are responsible for producing most of the cell's energy in the form of ATP. According to the endosymbiont theory, mitochondria began as separate bacteria that were absorbed into another cell for their energy-producing capabilities. video https://cdn.kastatic.org/googleusercontent/S5WqTBjP99Zsg1Ymfi8hS3_dAjI2pA5Vdz43G-jCpGNNty3UH8MA-4g8716ltXjJQkjRIQr9kZ1fTgLDILB87XI Mitochondria Mitochondria are organelles that contain their own DNA, and have both inner and outer membranes. Mitochondria are often referred to as the "powerhouses of the cell" because they are responsible for producing most of the cell's energy in the form of ATP. According to the endosymbiont theory, mitochondria began as separate bacteria that were absorbed into another cell for their energy-producing capabilities. https://cdn.kastatic.org/ka-youtube-converted/i1dAnpSFbyI.mp4/i1dAnpSFbyI.mp4 861 Observation and identification of cells (plant and animal) using microscopy and photomicrographs https://www.khanacademy.org/science/cambridge-o-level-biology-cie/x2a084a90105205d2:cells/x2a084a90105205d2:observation-and-identification-of-cells-using-microscopy-and-photomicrographs/v/mitochondria 2023-08-17T23:33:36.770424498Z Mitochondria Uncover the intriguing details of mitochondria, known as the cell's powerhouse. Learn about their distinctive structure, including the outer and inner membranes, and their vital role in cellular respiration. Understand how these self-replicating organelles, equipped with their own genome, aid in ATP production and fuel the cell with energy. Visit us (http://www.khanacademy.org/science/healthcare-and-medicine) for health and medicine content or (http://www.khanacademy.org/test-prep/mcat) for MCAT related content. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video. Efrat Bruck video https://cdn.kastatic.org/googleusercontent/YWwKd0XLmGjx53X1tJHTYu02gIP9QDjQcGcnHv964huC4b2rGBgsFtaUYSbYT32kB5gUA4VwuNeIdYNEo5SNiqft Mitochondria Uncover the intriguing details of mitochondria, known as the cell's powerhouse. Learn about their distinctive structure, including the outer and inner membranes, and their vital role in cellular respiration. Understand how these self-replicating organelles, equipped with their own genome, aid in ATP production and fuel the cell with energy. Visit us (http://www.khanacademy.org/science/healthcare-and-medicine) for health and medicine content or (http://www.khanacademy.org/test-prep/mcat) for MCAT related content. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video. https://cdn.kastatic.org/ka-youtube-converted/K7IxN3EDqm4.mp4/K7IxN3EDqm4.mp4 911 Observation and identification of cells (plant and animal) using microscopy and photomicrographs https://www.khanacademy.org/science/cambridge-o-level-biology-cie/x2a084a90105205d2:cells/x2a084a90105205d2:observation-and-identification-of-cells-using-microscopy-and-photomicrographs/v/the-nucleus 2023-08-17T23:33:36.770424498Z The nucleus Let's learn about the structure and function of the eukaryotic cell's nucleus. Discover the role of the outer and inner membranes, the nucleoplasm, and the nuclear pore in isolating the nucleus and facilitating transport. Explore the nucleolus, the site of ribosome assembly, and its relationship with the endoplasmic reticulum. Visit us (http://www.khanacademy.org/science/healthcare-and-medicine) for health and medicine content or (http://www.khanacademy.org/test-prep/mcat) for MCAT related content. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video. video https://cdn.kastatic.org/googleusercontent/kfgM2pLZ9Ntavmanjgy6f-MRWrA5ePaGk7rKfw2uW1siP_5MpJHM1HujuZNMKUzdddErNLNmyHd-FdfqZ3h-yHE- The nucleus Let's learn about the structure and function of the eukaryotic cell's nucleus. Discover the role of the outer and inner membranes, the nucleoplasm, and the nuclear pore in isolating the nucleus and facilitating transport. Explore the nucleolus, the site of ribosome assembly, and its relationship with the endoplasmic reticulum. Visit us (http://www.khanacademy.org/science/healthcare-and-medicine) for health and medicine content or (http://www.khanacademy.org/test-prep/mcat) for MCAT related content. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video. https://cdn.kastatic.org/ka-youtube-converted/gGeC0ntvxR8.mp4/gGeC0ntvxR8.mp4 365 Observation and identification of cells (plant and animal) using microscopy and photomicrographs https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/membrane-permeability/v/cell-membrane-introduction 2023-06-22T15:57:36.106541556Z Cell membrane introduction The cell membrane is made up of phospholipids, which have a hydrophilic phosphate head, a glycerol backbone, and two hydrophobic fatty acid tails. The phospholipids form a bilayer with the hydrophilic heads facing outward. This bilayer is semi-permeable meaning that it allows some substances to pass through while blocking others. William Tsai video https://cdn.kastatic.org/googleusercontent/BOP_7ArtE_8sGQn0s_C1le8WEVsKbOwwXtTKspEfzLQwRw69WoSlfvbHynVF4NFZPZOOKxbloveEnONZ-Vl17J8 Cell membrane introduction The cell membrane is made up of phospholipids, which have a hydrophilic phosphate head, a glycerol backbone, and two hydrophobic fatty acid tails. The phospholipids form a bilayer with the hydrophilic heads facing outward. This bilayer is semi-permeable meaning that it allows some substances to pass through while blocking others. https://cdn.kastatic.org/ka-youtube-converted/QpcACa39YtA.mp4/QpcACa39YtA.mp4 532 Observation and identification of cells (plant and animal) using microscopy and photomicrographs https://www.khanacademy.org/science/cambridge-o-level-biology-cie/x2a084a90105205d2:cells/x2a084a90105205d2:observation-and-identification-of-cells-using-microscopy-and-photomicrographs/v/phospholipid-structure 2022-11-16T04:22:43.7414897Z Phospholipid structure Phospholipids are molecules that form the cell membrane. They consist of a polar phosphate head group and two nonpolar fatty acid tails joined by a glycerol backbone. The phosphate group can link with different molecules, such as serine or choline, to generate diverse kinds of phospholipids. The fatty acid tails can have cis or trans double bonds, which influence the membrane fluidity. The molecular details of phospholipids and their variations can be drawn as shown. William Tsai video https://cdn.kastatic.org/googleusercontent/uQOBLlmptyMTcMQRRiDQ9tKsQZ4M1A_kCJ2y9W_inQ2mDyuQBgHo5eP9EtievnkolvgL0lGP72lzQ0GYTWFJ4VFc Phospholipid structure Phospholipids are molecules that form the cell membrane. They consist of a polar phosphate head group and two nonpolar fatty acid tails joined by a glycerol backbone. The phosphate group can link with different molecules, such as serine or choline, to generate diverse kinds of phospholipids. The fatty acid tails can have cis or trans double bonds, which influence the membrane fluidity. The molecular details of phospholipids and their variations can be drawn as shown. https://cdn.kastatic.org/ka-youtube-converted/CBEys2CTkgE.mp4/CBEys2CTkgE.mp4 421 Observation and identification of cells (plant and animal) using microscopy and photomicrographs https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/membrane-permeability/v/cell-membrane-overview-fluid-mosaic-model 2023-08-14T21:12:46.061619254Z Cell membrane overview and fluid mosaic model Learn about the cell membrane's vital role in regulating what enters and leaves a cell, and in helping a cell successfully maintain homeostasis, even when the environment around it is changing. Explore the cell membrane's the three main components: phospholipids, cholesterol, and proteins. Learn how these elements form the fluid mosaic model, allowing for movement and flexibility, and explore the functions of proteins as receptors and transporters, and the importance of carbohydrates in cell recognition. By William Tsai. William Tsai video https://cdn.kastatic.org/googleusercontent/R8xJgaoGc1j5iIiBx6HgdJWM4660o02sUhB2PVGebfF42JfL_pUqzZ3IRTYbUzM99BRKNFnrcee2jmTpI95sIVJK Cell membrane overview and fluid mosaic model Learn about the cell membrane's vital role in regulating what enters and leaves a cell, and in helping a cell successfully maintain homeostasis, even when the environment around it is changing. Explore the cell membrane's the three main components: phospholipids, cholesterol, and proteins. Learn how these elements form the fluid mosaic model, allowing for movement and flexibility, and explore the functions of proteins as receptors and transporters, and the importance of carbohydrates in cell recognition. By William Tsai. https://cdn.kastatic.org/ka-youtube-converted/LXaPt9i9hqk.mp4/LXaPt9i9hqk.mp4 532 Observation and identification of cells (plant and animal) using microscopy and photomicrographs https://www.khanacademy.org/science/cambridge-o-level-biology-cie/x2a084a90105205d2:cells/x2a084a90105205d2:observation-and-identification-of-cells-using-microscopy-and-photomicrographs/v/cell-membrane-fluidity 2022-11-16T04:22:43.7414897Z Cell membrane fluidity Cell membrane fluidity is the property of the cell membrane that allows it to adapt its shape and movement to different conditions. Three key factors influence cell membrane fluidity: temperature, cholesterol, and the kind of fatty acids in the phospholipids that form the cell membrane. These factors alter the space and interaction between the phospholipids, and how this affects the fluidity of the cell membrane. William Tsai video https://cdn.kastatic.org/googleusercontent/EkboMM7-i1JD4jUEa4Kq0I2a-Gveyh-0gMlu8OF6ENLzXgZ4Jfhqj1pmZ4-rpYo71X9l-cv2YlDrqDp7529xIuNQ Cell membrane fluidity Cell membrane fluidity is the property of the cell membrane that allows it to adapt its shape and movement to different conditions. Three key factors influence cell membrane fluidity: temperature, cholesterol, and the kind of fatty acids in the phospholipids that form the cell membrane. These factors alter the space and interaction between the phospholipids, and how this affects the fluidity of the cell membrane. https://cdn.kastatic.org/ka-youtube-converted/BWQCAsM-CF4.mp4/BWQCAsM-CF4.mp4 424 Observation and identification of cells (plant and animal) using microscopy and photomicrographs https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/plasma-membranes/v/cell-membrane-proteins 2023-08-14T21:12:46.061619254Z Cell membrane proteins Proteins comprise 75% of the cell membrane's mass, and play key roles in cellular processes. Explore the differences between integral, peripheral, and lipid-bound proteins, and discover how channel and carrier proteins maintain cellular balance. You'll also learn about the signaling role of glycoproteins in cell recognition. By William Tsai. William Tsai video https://cdn.kastatic.org/googleusercontent/apCfEj1gUWIR3E9wGxY7XzqUewYBAVc-JyfgZjgHf4_79mECtkMtSgZ6fcuKpsEWwcNrVq2rTi5PwhhF6Mtkt70Gnw Cell membrane proteins Proteins comprise 75% of the cell membrane's mass, and play key roles in cellular processes. Explore the differences between integral, peripheral, and lipid-bound proteins, and discover how channel and carrier proteins maintain cellular balance. You'll also learn about the signaling role of glycoproteins in cell recognition. By William Tsai. https://cdn.kastatic.org/ka-youtube-converted/0emD1AmfdjY.mp4/0emD1AmfdjY.mp4 491 Observation and identification of cells (plant and animal) using microscopy and photomicrographs https://www.khanacademy.org/science/cambridge-o-level-biology-cie/x2a084a90105205d2:cells/x2a084a90105205d2:observation-and-identification-of-cells-using-microscopy-and-photomicrographs/v/lysosomes-and-vacuoles-pk 2025-12-18T03:40:48.390254156Z Lysosomes and vacuoles Created by Khan Academy video https://cdn.kastatic.org/googleusercontent/ZCdwTudJg6e6n-P2gsaUborP4izvMsGo71pvEVlX9dNYWcLXcP7VHkWpn2grt4TUP1KoJLQP9NswyHBuBLSFTBw Lysosomes and vacuoles Created by Khan Academy https://cdn.kastatic.org/ka-youtube-converted/ngmm-NtxJNU.mp4/ngmm-NtxJNU.mp4 692 Observation and identification of cells (plant and animal) using microscopy and photomicrographs https://www.khanacademy.org/science/ms-biology/x0c5bb03129646fd6:cells-and-organisms/x0c5bb03129646fd6:cell-parts-and-functions/v/comparing-animal-and-plant-cells 2022-10-21T22:40:33.613234713Z Comparing animal and plant cells Plant cells have a cell wall in addition to a cell membrane, whereas animal cells have only a cell membrane. Plants use cell walls to provide structure to the plant. Plant cells contain organelles called chloroplasts, while animal cells do not. Chloroplasts allow plants to make the food they need to live using photosynthesis. Khan Academy video https://cdn.kastatic.org/ka_thumbnails_cache/56d3be07-e2e3-4665-9da5-d5ced92c2ef9_1280_720_base.png Comparing animal and plant cells Plant cells have a cell wall in addition to a cell membrane, whereas animal cells have only a cell membrane. Plants use cell walls to provide structure to the plant. Plant cells contain organelles called chloroplasts, while animal cells do not. Chloroplasts allow plants to make the food they need to live using photosynthesis. https://cdn.kastatic.org/ka-youtube-converted/HjC-eMiMDfo.mp4/HjC-eMiMDfo.mp4 237 Observation and identification of cells (plant and animal) using microscopy and photomicrographs https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/membrane-permeability/v/plant-cell-walls 2022-11-16T04:22:43.7414897Z Plant cell walls The cell wall surrounds the plant cell, providing both structure and protection. Plant cell walls are made up mostly of cellulose, and also include hemicellulose and pectin. Plant cells connect directly to one another via tunnels in their cell walls called plasmodesmata. video https://cdn.kastatic.org/googleusercontent/f1qMxaZZgQlEIw_d6Y37Y2BWCKKcj5_x5ck6SHI1VgGVR8OkAd76PhcPj3EMDrUKh_gWIdaTOh9Ro8-mGCYsVdHC Plant cell walls The cell wall surrounds the plant cell, providing both structure and protection. Plant cell walls are made up mostly of cellulose, and also include hemicellulose and pectin. Plant cells connect directly to one another via tunnels in their cell walls called plasmodesmata. https://cdn.kastatic.org/ka-youtube-converted/zdvKhaQxvag.mp4/zdvKhaQxvag.mp4 463 Observation and identification of cells (plant and animal) using microscopy and photomicrographs https://www.khanacademy.org/science/hs-bio/x230b3ff252126bb6:from-cells-to-organisms/x230b3ff252126bb6:the-cellular-basis-of-life/a/cell-biology-and-microscopy 2025-11-07T05:50:37.873729281Z Cell biology and microscopy Learn about cell biology and the different types of microscopes that allow us to observe cell structure and function. article https://www.khanacademy.org/science/ms-biology/x0c5bb03129646fd6:cells-and-organisms/x0c5bb03129646fd6:cells-organisms/a/cells-and-organisms 2026-04-15T10:00:48.515869037Z Key points: Cells and organisms Review your understanding of cells and organisms in this free article. article https://www.khanacademy.org/science/biology/structure-of-a-cell/prokaryotic-and-eukaryotic-cells/a/nucleus-and-ribosomes 2021-04-29T07:56:45Z Nucleus and ribosomes Structure and function of the nucleus and ribosomes of a cell. How they work together in the production of proteins. article https://www.khanacademy.org/science/biology/structure-of-a-cell/prokaryotic-and-eukaryotic-cells/a/plasma-membrane-and-cytoplasm 2021-04-29T08:00:32Z Plasma membrane and cytoplasm Structure and function of the plasma membrane and cytoplasm of cells. Also covers the phospholipid bilayer and microvilli. article https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/membrane-permeability/a/fluid-mosaic-model-cell-membranes-article 2022-05-13T20:48:32.676099881Z Fluid mosaic model: cell membranes article article https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/cell-compartmentalization-and-its-origins/a/chloroplasts-and-mitochondria 2026-01-28T06:30:36.172736652Z Mitochondria and chloroplasts Structure and function of mitochondria and chloroplasts. Endosymbiosis. article https://www.khanacademy.org/science/ms-biology/x0c5bb03129646fd6:cells-and-organisms/x0c5bb03129646fd6:cell-parts-and-functions/e/understand-cell-parts-and-functions 2026-04-02T04:15:35.616513959Z Understand: cell parts and functions Check your understanding of cell parts and functions in this set of free practice questions aligned to NGSS standards. Khan Academy exercise https://www.khanacademy.org/science/ms-biology/x0c5bb03129646fd6:cells-and-organisms/x0c5bb03129646fd6:cell-parts-and-functions/e/apply-cell-parts-and-functions 2026-02-27T17:50:36.702607024Z Apply: cell parts and functions Apply your understanding of cell parts and functions in this set of free practice questions aligned to NGSS standards. Khan Academy exercise https://www.khanacademy.org/science/cambridge-o-level-biology-cie/x2a084a90105205d2:cells/x2a084a90105205d2:observation-and-identification-of-cells-using-microscopy-and-photomicrographs/e/cell-membrane-questions 2025-04-14T22:34:53.782134477Z Cell membrane questions Cell membrane questions Jeff Collins exercise