Biology Unit 4:�Cell Structure & Function

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Discovery of Cells

• 1600’s
• Robert Hooke

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• 1820’s: Rene Dutrochet

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• 1830’s: Robert Brown
• Matthias Schleiden
• Theodore Schwann
• Rudulph Virchow

• Discovery of light microscope
• Named box-like structures in cork “cells”
• Cells are found in various parts of organisms
• All cells have a nucleus
• All plants are composed of cells
• All animals are composed of cells
• All cells come from living cells

Cell Theory

Three parts:

• All living things are made of cells
• The cell is the basic unit of structure and function in living things
• All cells come from existing cells

Unicellular Organisms

• Cell is the organism
• In terms of numbers > dominate life on Earth

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Yeast

Volvox aureus

Euglena

Chlamydomonas

Multicellular Organisms

• Made up of many cells
• Great variety of organisms
• All depend on specialized cells
• Cells develop in different ways to perform different tasks
• Ex: Red blood cells transport oxygen throughout body

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Red blood cells

Multicellular Organisms (cont.)�Levels of organization

• Cell - Ex: muscle cell
• Tissue - group of similar cells perform a particular function
• Ex: muscle tissue
• Organ - group of tissues that work together
• Ex: stomach
• Organ system - group of organs that work together to perform specific function
• Ex: digestive system

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Smooth muscle tissue

Muscle cell

Stomach

Digestive System

Types of Cells

• Eukaryotic
• Genetic material contained in nucleus
• Plants, animals, fungi and protists
• Prokaryotic
• Genetic material NOT contained in nucleus (*No nucleus*)
• Bacteria

The Eukaryotic Cell

Cell Structure

• Like a factory
• Two major parts: cytoplasm & nucleus
• Organelles (“little organs”)
• Act like specialized organs
• Some structures developed from early prokaryotes
• Ex: mitochondria & chloroplasts

Cytoplasm

• Gelatin-like material inside the cell membrane, outside the nucleus
• Contains organelles
• Site of most cell activity
• Factory floor where products are assembled, finished & shipped

Nucleus

• Control center of the cell > boss or CEO
• Responsible for overall function of factory
• Determines what proteins will be made
• Contains hereditary information > DNA

Nucleolus

• Small, dense region of nucleus
• Assembly of ribosomes begins here

Nuclear Envelope

• Membrane around nucleus only
• Has small pores that allow information and ribosomes to move in and out of nucleus

Ribosomes

• Responsible for assembling proteins
• Workers on assembly line in factory
• Responds to orders from boss > nucleus
• Located throughout cytoplasm

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Endoplasmic Reticulum

• Site where lipid components of cell membrane are assembled
• Also assembles proteins exported from cell
• Assembly line in factory
• Two types:
• Rough ER - appears bumpy due to ribosomes on surface
• Smooth ER - No ribosomes

Endoplasmic Reticulum

Golgi Apparatus

• Prepares proteins and other materials for storage or use outside cell
• Like finishing & packing department in factory
• Finishing touches put on before ready to leave factory
• Sorted & stored or shipped outside of cell

Lysosomes

• Small organelles filled with enzymes
• Maintenance crew for factory
• Break down carbs, lipids & proteins for use by cell
• Remove “junk” - waste and dead material found in cell

Vacuoles

• Saclike structures that store nutrients
• water, salts, proteins & carbs
• Storage rooms of factory

Mitochondria

• Convert nutrients in food into energy for cell use
• Local power plant for factory
• Source of energy

Chloroplasts

• Capture energy from sunlight and convert it into chemical energy > photosynthesis
• Solar power source for factory
• Only in plant cells
• Chlorophyll > chemical that causes plant cells to be green

Cytoskeleton

• Network of protein fibers that helps cell maintain its shape
• Microtubules and microfilaments
• Support structure of factory (beams & columns that support walls & roof)
• Also used to move cell membrane

Cell Membrane

• Phospholipid bilayer
• Regulates what enters & leaves the cell
• Like gate into the factory
• Provides protection & support
• Gives the cell its shape

Cell Wall

• Outside cell membrane
• Provides protection & support
• Present in plants, algae, fungi and many prokaryotes
• Never in animal cells

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Plant Cell

Cell Wall (algae)

Cell Wall (bacteria > prokaryote)

Movement Across Cell Boundaries

Diffusion

• Molecules spread into available space
• across membrane
• from area of higher concentration to area of lower concentration
• without use of energy > passive transport
• Equilibrium - when concentration is same throughout a system

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Osmosis

• Diffusion of water through a selectively permeable membrane
• Membrane allows only certain substances to pass through
• Type of diffusion - does not require use of energy > passive transport

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How Osmosis Works

• Isotonic - “same strength”
• Same concentration on both sides
• Hypertonic - “above strength”
• Higher concentration outside cell
• Water leaves, cells shrink
• Hypotonic - “below strength”
• Lower concentration outside cell
• Water comes in, cells swell

http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm

Facilitated Diffusion

• Movement of specific molecules across membranes through transport proteins
• Could not cross without them
• Does not require use of energy > passive transport

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Active Transport

• Cells move materials in direction opposite diffusion
• Against concentration difference (gradient)
• Requires energy
• Small molecules or ions (K, Ca, Na) carried by transport proteins or “pumps” in membrane

Active Transport (cont.)

Larger molecules & clumps of material transported by:

• Endocytosis - movement of materials into cell through vesicles (pockets) of cell membrane
• Phagocytosis- “cell eating”
• Pinocytosis- “cell drinking”
• Exocytosis - movement of materials out of cell through vesicles

IV. Homeostasis

1. The Cell as an Organism
1. Unicellular organism- organism made up of only one cell
1. Examples:
1. Bacteria
2. Yeast
3. protists- amoeba, diatoms, plasmodium

b. Exhibit all 8 features of living things

c. All organisms must maintain homeostasis

• Defined- relatively constant internal; physical and chemical conditions

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B. Multicellular Life

1. Cells in multicellular organisms do not live on their own

2. They are interdependent- need to work together

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3. Need to communicate- send and receive signals with each other

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4. Cell specialization- different types of cells play different roles

1. Some move- throat lining cells
2. Some react- nerve cells
3. Some produce substances- glandular cells

5. Levels of Organization�cells --> tissues --> organs --> organ systems --> organisms

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a. Tissue – is a group of similar cells that work together to perform a function.

Nerve Cell

Nerve Tissue

Examples of Tissues

b. Organ – is a group of tissues that work together to do a job.

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c. Organ system- is a group of organs that work together to do a certain job.

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d. Organism – is a living thing that can be made of one or more cells.

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Examples of organisms

Amoeba

Crow

Elephant

Bonobo

Human

6. Cellular Communication

1. Cells in large organisms communicate by means of chemical signals
2. The signals can either speed up or slow down an activity of the cells that are receiving them
3. Cellular junctions- hold cells together in tight formations that allow for quick signaling
1. Ex: neuromuscular junction

d. Receptor- can be found on or in a cell; a specific protein whose shape fits that of a molecular messenger

• Ex: Hormones

Thyroid Hormone Receptor

Thyroid gland is controlled chemically by the pituitary- function: metabolism

Careers that study cells and/or tissues

• Histologist- tissues/cells
• Pathologist- infected tissues/cells
• Oncologist- cancer cells
• Embryologist- examines infertility
• Geneticist
• Veterinarian