Cell Energy

Middle School Science

Moving materials in cells

  Cells need energy 24/7 They cannot make their own, but can change energy from one form to another  Cells obtain energy from their environment and convert it to a usable form  Complex process

Moving materials in cells

 Metabolism  The sum of all activities within a cell   Cannot just happen Need raw materials   Need to eliminate waste All material needs to enter and exit through the cell membrane

Moving materials in cells

 Materials enter and leave a cell by one of three methods:   Diffusion Osmosis  Active transport

Diffusion

 Cell membranes in living things need to allow materials to pass through   Selectively-permeable membrane Substances pass through the pores  Driving force behind the movement of many substances into or out of the cell is diffusion

Diffusion

 The process by which molecules of a substance move from areas of higher concentration of that substance to areas of lower concentration of that substance

Diffusion

 What causes diffusion to occur?

 Mainly small molecules  Driving force behind movement  All molecules are in motion    Solids – molecules move slowly Liquids – move more quickly Gases – move quickly  Molecules collide with each other, pushing away from one another

Diffusion

 What causes diffusion to occur?

 Driving force behind movement  Collisions will continue as molecules spread out evenly

Diffusion

 Why don’t the organelles and cytoplasm pass through the cell membrane?

 Cell membrane is selectively permeable  Permits only certain substances to diffuse  Oxygen, water, and food molecules are permitted to diffuse into the cell  Carbon dioxide and other waste materials are permitted to diffuse out of the cell

Osmosis

 A special kind of diffusion  The diffusion of water across a selectively permeable membrane = osmosis  Water is the most important substance that passes through a cell membrane  About 80% of the cell is water

Diffusion and Osmosis

 Diffusion and osmosis are types of passive transport  They do not require energy to be able to happen – they just happen

Active Transport

 What if the cell needs materials that cannot diffuse through the membrane?

 Active transport “carries” the materials into or out of the cell   Cells have several forms of active transport Transport proteins can “pick up” molecules and carry them into or out of the cell  Requires energy  Ex: calcium, potassium, and sodium

Active Transport

 What if the cell needs materials that cannot diffuse through the membrane?

 Transport by engulfing  Another method of active transport  Cell membrane surrounds, or engulfs, a particle  Once surrounded, the cell membrane wraps around the particle and forms a vacuole within the cell  Requires energy

Cell Growth and Division

 Limits on Cell Growth  Why don’t cells get bigger and bigger?

 Has to do with the transportation of materials into and out of the cell  If a cell were to get too large, its membrane would not be able to handle the flow of materials passing through it   The amount of raw materials needed by a large cell couldn’t enter fast enough The wastes produced couldn’t leave fast enough

Cell Division

 In order for an organism to grow, the total number of cells must increase  Cell division  One cell divides into two new daughter cells  Occurs in a series of stages, or phases  The process of cell division = mitosis

Mitosis

 Phase 1: Chromosomes are copied  Interphase  Cell is performing life functions, not dividing  Chromosomes appear as threadlike coils called chromatin  In animal cells, the two centrioles can be seen outside the nucleus  Most plant cells do not have centrioles

Mitosis

 Phase 1  Near the end, the process of cell division begins  The chromosomes are duplicated  Doubling the normal chromosome number in the cell  Each chromosome and its sister chromosome (copy) are attached at an area called the centromere  At this time the sister chromosomes are called chromatids

Mitosis

 Phase 2: Mitosis begins  Prophase  Mitosis begins  Mitosis = the process by which the nucleus of a cell divides into two nuclei and the formation of two new daughter cells begins  Threadlike chromatin shorten and form rodlike chromosomes   Centrioles begin to move to opposite ends of cell Meshlike spindle develops, forming a bridge between opposite ends of the cell

Mitosis

 Phase 3: Chromosomes attach to the spindle  Metaphase  The chromosomes begin to attach to the spindle  Chromosomes are attached to the spindle by the centromere, which still connects each chromatid to its identical sister chromatid

Mitosis

 Phase 4: Chromosomes begin to separate  Anaphase  The centromere splits  The sister chromatids separate from each other  Chromatids move to opposite ends of cell along the spindle  The chromatids are again called chromosomes at this point

Mitosis

 Phase 5: Two new nuclei form  Telophase  The chromosomes begin to uncoil and lose their rodlike appearance  A nuclear membrane forms around the chromatin at each end of the cell  In each nucleus, a nucleolus reappears  At this point, mitosis is complete but the cell still has one phase to go through

Mitosis

 Phase 6: Two daughter cells form  Cytokinesis    Final phase of cell division Involves the division of the cytoplasm The membrane surrounding the cell begins to move inward until the cytoplasm is pinched in two  Each part contains a nucleus with identical chromosomes  The cell membrane (or cell wall) complete the division

Mitosis

Mitosis