Cells Unit 4

Levels of Organization 1. Organelle - structure that has a specific function in the cell 2. Cell – basic unit of life 3. Tissue - group of cells working together to perform a common function 4. Organ - tissues working together 5. Organ System - group of organs working together 6. Organism - entire living being

Development of the Cell Theory Early 1600s – Invention of the light microscope This allowed people to see life at a microscopic level! 1665: Hooke: looked at cork (a plant) under a microscope and called the boxes he saw “cells” 1683: Leeuwenhoek: made a better light microscope that could magnify up to 200X. He was the first to observe small single-celled organisms. 1838: Schleiden: plants are made of cells 1839: Schwann: animals are made of cells 1858: Virchow: cells come from pre-existing cells

Better Technology = Better Understandings Development of better technology like electron and scanning microscopes show more detail so we can observe parts of the cells and cellular processes.

The Cell Theory Living things are composed of one or more cells. Cells are the basic units of structure and function of living things. New cells arise from pre-existing cells.

Main Jobs of Cells Cells perform chemical reactions so that organism can: Acquire energy Reproduce Maintain homeostasis (stable internal environment) Produce proteins for growth and repair

Prokaryotic v. Eukaryotic Cells The simplest life forms are prokaryotes. These are single-celled organisms that were the earliest life on Earth. Prokaryotic cells exist in two major forms: bacteria and archaea. Prokaryotes are Earth’s most abundant inhabitants. Eukaryotes arose from prokaryotes and developed into larger, more complex organisms, like protists, fungi, plants, and animals. Eukaryotes have many cell structures (organelles) that perform a specific function.

Organelles Nucleus Contains DNA, site where RNA is made Nucleolus – dark region where ribosomes are assembled. Mitochondria Site of cell respiration (breaks down energy sources - “powerhouse”)

Organelles Ribosome Site of protein synthesis (production) Endoplasmic Reticulum (Rough or Smooth) Transports materials through the cell. Rough ER has ribosomes. Golgi Apparatus Site where cell products are packaged for export

Organelles Lysosome Contains digestive enzymes Vacuole Storage of food, water, or wastes. Plants have 1 central vacuole, animals have many small vacuoles. Chloroplasts (plant only) Site of photosynthesis (uses sun’s energy to make glucose) Centrioles (animal only) Organize spindle fibers during cell division.

Organelles Cytoplasm Fluid inside the cell that contains organelles and is the site of many reactions Cell (Plasma) membrane Controls what enters and leaves the cell. Made of phospholipid bilayer. Cell wall (plants only) Provides support (for plant cells) Cytoskeleton Helps maintain cell shape (made of microfilaments and microtubules)

Organelles Structures for cell movement: Cilia Many short hair-like projections that draw materials in towards cell Flagella Long whip-like tail that moves cell through surroundings Pseudopodia *Not really an organelle! Temporary extension of cytoplasm that allows cell to drag itself in one direction

Unicellular vs. Multicellular Organisms Some organisms exist as a single cell (unicellular), while others are composed of many cells (multicellular). All organisms need to perform the same functions to survive. A single-celled organism has to conduct all processes in one cell. However, a multicellular organism has groups of cells that specialize to perform specific functions (ex. - skin cells, muscle cells, brain cells…).

Two Types of Cells Prokaryote Eukaryote Simple, smaller NO nucleus or membrane-bound organelles Ex) bacteria More complex, larger Has nucleus and membrane-bound organelles Ex) plants, animals, fungi

Plant vs. Animal Cells Animal Cells Plant Cells No cell wall Cell wall Both eukaryotic cells! Animal Cells No cell wall Many small vacuoles Contain centrioles for cell division Rounded irregular shape Plant Cells Cell wall Have chloroplasts One central vacuole Fixed, rectangular shape

Plant vs. Animal Cells Foldable Fold so that plant and animal cell halves meet in the middle Label organelles On the inside, list name and function of – Shared organelles in the middle Plant only organelles on the left Animal only organelles on the right

Unit 4 The Light Microscope

Light Microscopes Light passes through lenses to produce an enlarged image of a specimen.

Magnification v. Resolution Magnification: ability to make an object appear larger (“zoom” in) Resolution: how clear the image is To calculate the total magnification: Eyepiece: magnifies specimen 10x by itself Objectives : 4x, 10x, 20x, 40x, 100x Total Magnification: Eyepiece x Objective Ex) total magnification of 40x objective is 10x40 = 400x

Parts of the Microscope A. Eyepiece B. Objective (lens) C. Stage D. Course Adjustment E. Fine Adjustment F. Arm or Neck G. Light source H. Base

Review – Label each organelle

The Cell Membrane and Cell Transport Unit 4 The Cell Membrane and Cell Transport

Functions of the Cell Membrane All cells are surrounded by a cell membrane – also called the plasma membrane or phospholipid bilayer Function: Maintains homeostasis – stable internal conditions Controls movement of materials in and out of the cell - selectively permeable means that the membrane only allows some materials through, not all Communication between cells Recognition of cells

Structure of the Cell Membrane The fluid mosaic model says that the cell membrane is made of different components that move around. Double layer of phospholipids: lipids that have charged phosphate heads – main component of membrane Cholesterol: stabilizes the membrane Transport proteins: allow specific molecules through Carbohydrates: important for cell recognition 1 2 4 3

Phospholipid Structure Polar Heads: hydrophilic (like water)- always face outside or inside of cell Fatty Acid Tails: hydrophobic (doesn’t like water)- always face inside of membrane Fluidity Animation Inside and outside environment of cells are mostly water. Hydrophobic tails are repelled by this water and orient themselves in a double layer.

Cell Transport Movement of materials in and out of cell. Concentration gradient – the difference in concentration inside the cell vs. outside. Materials can move down concentration gradient (from high to low) on their own (passive transport). Cells must use energy to move materials from areas of low concentration to high (active transport).

Passive Transport Does NOT require energy to move molecules from areas of HIGH concentration  LOW Diffusion Facilitated Diffusion Osmosis

Types of Passive Transport Diffusion: substances move from an area of higher to lower concentration. Facilitated diffusion: larger substances are moved from high to low with the assistance of a transport protein (still no energy used!) Osmosis: movement of water through a semi-permeable membrane Small, neutral molecules can move straight through membrane phospholipids – oxygen, carbon dioxide Large or charged molecules must go through protein channels – glucose, amino acids

Dynamic Equilibrium Through passive transport, molecules will reach equilibrium where the concentration inside is the same as outside the cell Dynamic Equilibrium: molecules continue to move back and forth equally but there is no net change in concentration.

Active Transport Active transport: movement of solid or liquid particles in and out of a cell that requires input of energy (ATP). Move large particles and remove wastes. Move materials against concentration gradient (low  high concentration).

Types of Active Transport Protein pump: membrane protein uses energy to move materials (from low to high) Endocytosis: membrane pinches in to take particles into the cell Pinocytosis: liquids in Phagocytosis: solids in Exocytosis: particles surrounded by membrane are moved out of cell

Cell Transport Summary Osmosis (Water)

Solutions Most membranes are permeable to water, but not permeable to many solutes. Solvent – Dissolving agent (ex. Water) Solute – Substance that is dissolved (ex. Kool aid mix) If the concentration of solutes is different on the inside and outside of a cell, water will move across the membrane to equalize the concentrations.

How Osmosis Works Click for animation

Hypertonic Solutions: contain a high concentration of solute Hypertonic Solutions: contain a high concentration of solute. When a cell is placed in a hypertonic solution, the water diffuses out of the cell, causing the cell to shrink. Hypotonic Solutions: contain a low concentration of solute. When a cell is placed in a hypotonic solution, the water diffuses into the cell, causing the cell to swell. Isotonic Solutions: contain the same concentration of solute as the cell. When a cell is placed in an isotonic solution, the water diffuses into and out of the cell at the same rate. The fluid that surrounds body cells is isotonic.

Turgor Pressure Water pushing out on the plant cell wall – helps give plants their shape. This is why plants wilt if they don’t get enough water 36

B C A What type of solution are these cells in? Hypertonic Isotonic Hypotonic 37

Surface Area to Volume Ratio As cells increase in size, surface area to volume ratios decrease. This makes cells unable to obtain nutrients or remove wastes (bigger cells = less efficient). To increase surface to volume ratio, cells divide to stay small or change shape in order to increase surface area or reduce volume (smaller cells = more efficient). *Small cell = LARGE surface area to vol. ratio *Large cell = SMALL surface area to volume ratio

Three Types of Solutions 90% H2O 10% solute 90% H2O 10% solute 90% H2O 10% solute 90% H2O 10% solute 95% H2O 5% solute 85% H2O 15% solute Hypotonic Hypertonic Isotonic (no net movement of water)

Passive Transport Review Animation