The Cell in Action Ms. Samuelian

Exchange with the Environment A cell must be able to obtain energy and raw materials and get rid of wastes The exchange of materials between a cell and its environment takes place at the cell’s membrane Before we study about how materials move into and out of the cell, we need to understand diffusion (a process that affects the movement of particles)

Diffusion

Diffusion What would happen if you pour dye into a container of solid gelatin? Over time the line between the layers will become blurry because the tiny particles move and collide with each other Particles naturally travel from areas where they are crowded to areas where they are less crowded. This kind of movement is called diffusion Diffusion is the movement of particles from an area where their concentration is high to an area where their concentration is low

Osmosis All organisms need water to live The cells of living organisms are surrounded by and filled with fluids that are made mostly of water The diffusion of water through the cell membrane is called osmosis

Moving Small Particles Many particles, such as water and oxygen, can diffuse directly through the cell membrane However, not all of the particles a cell needs can pass through the membrane in this way Sugar and amino acids aren’t small enough to squeeze through They must travel through protein “doorways” located in the cell membrane in order to enter and leave the cell Particles can travel through these proteins either by passive transport or by active transport

Passive Transport In passive transport, particles travel through proteins The particles move from an area of high concentration to an area of low concentration The cell does not need to use any energy to make this happen

Active Transport Active transport is the movement of particles through proteins against the normal direction of diffusion Particles are moved from an area of low concentration to high concentration The cell must use energy to make this happen This energy comes from the molecule ATP, which stores energy in a form that cells can use

Moving Large Particles Diffusion, passive transport, and active transport are good methods of moving small particles into and out of cells, but what about moving large particles? The cell membrane has two ways of accomplishing this task: endocytosis and exocytosis Endocytosis means “within a cell” Exocytosis means “outside the cell”

Endocytosis In endocytosis, the cell membrane surrounds a particle and encloses it in a vesicle This is how large particles, such as other cells, can be brought into a cell

Exocytosis When a large particle must be removed from the cell, the cell uses a different process In exocytosis, vesicles are formed at the endoplasmic reticulum or Golgi complex and carry the particles to the cell membrane.

Review Questions During diffusion, do particles move from areas of low concentration to areas of high concentration or from areas of high concentration to areas of low concentration? How does a cell take in large particles? How does a cell expel large particles?

Cell Energy Why do you get hungry? Feeling hungry is your body’s way of telling you that your cells need energy Your cells and the cells of all organisms use energy to carry out the chemical activities that allow them to live, grow, and reproduce

From Sun to Cell Nearly all of the energy that fuels life comes from the sun Your cells get energy from the foods you eat You must eat plants or eat organisms that have eaten plants This is because plants are able to capture light energy from the sun and change it into food through a process called photosynthesis

Photosynthesis Photosynthesis means “made by light” Plants have molecules (called pigments) in their cells that absorb the energy of light Chlorophyll (the main pigment used in photosynthesis) gives plants their green color Plants use the energy captured by chlorophyll to change carbon dioxide and water into food The food that is produced is the simple sugar glucose When plants make glucose, they are converting the sun’s energy into a form of energy that can be stored Photosynthesis also produces oxygen

Getting Energy from Food The food you eat has to be broken down so that the energy it contains can be converted into a form your cells can use There are two ways to do this: One way uses oxygen and is called cellular respiration The other way does not use oxygen and is called fermentation

Cellular Respiration Most organisms use cellular respiration to obtain energy that is stored into food During cellular respiration, food (glucose) is broken down into carbon dioxide and water, and energy is released A lot of the energy is stored in the form of ATP ATP is the molecule that supplies energy to fuel the activities of cells In the cells of plants, animals, and other eukaryotic cells, cellular respiration takes place in mitochondria

Fermentation Have you ever run so far that you started to feel a burning sensation in your muscles? Sometimes your muscle cells can’t get the oxygen they need to produce ATP by cellular respiration When this happens, they use the process of fermentation Fermentation leads to the production of a small amount of ATP from the partial breakdown of glucose

Did You Know? When the Earth was young, its atmosphere lacked oxygen. The first forms of life used fermentation to gain energy. After organisms evolved the ability to photosynthesize (about 3 billion years ago) the oxygen they produced was added to the atmosphere Thrombolites are rock-like structures built by micro-organisms. Often regarded as the earliest geographical features of primitive life on Earth, they are in fact bacteria which deposit layers of silt and calcium that slowly grow into rounded rocks. Scientists believe these micro-organisms are the earliest form of life on earth. Millions of years ago, there was no oxygen in the atmosphere and no protective ozone layer. According to researchers, this began changing when the tiny organisms started to appear. They lived in water and produced oxygen which gradually and very slowly built up the atmosphere we know today.

Count to 10… Do you know what just happened during those 10 seconds Count to 10… Do you know what just happened during those 10 seconds? Your body produced millions of new cells!

Producing new cells allows you to grow and replace cells that have died Your cells pass through different stages in their life cycle known as the cell cycle The cell cycle begins when the cell is formed and ends when the cell divides and forms new cells Before a cell divides, it must make a copy of its DNA and other materials that are needed to carry out the processes of life

Remember: DNA contains the information that tells a cell how to make proteins The DNA of a cell is organized into structures called chromosomes Copying chromosomes ensures that each new cell will have all of the necessary tools for survival

Cell Division Before cell division begins, DNA forms chromosomes, and copies are made of each chromosome After copying, each chromosome has an identical sister chromosome Pairs of identical sister chromosomes are called chromatids Cell division occurs in two stages: mitosis and cytokinesis

Mitosis Mitosis is the first stage of cell division In eukaryotic cells, this is the stage in which the nucleus divides Mitosis occurs in 4 phases: prophase, metaphase, anaphase, and telophase