Chapter 2

Cells

Comparing Cells

• Cells differ in size and shape depending on their function– Ex: nerve cell needs to

communicate between places, so it is a long cell

– Ex: a muscle cell can contract and change it’s shape

• Two cell types:• Prokaryotic – lack membrane-

bound internal structures• Eukayrotic – contain

membrane-bound internal structures

Cell Organization

Cell wall– Tough, rigid outer coverings that

protect the cell and give it shape– Made of cellulose– Only in plants, algae, fungi and

most bacteria– “frame of a house”

• Cell Membrane– A protective layer around all cells– Inside the cell wall, if it is present– Allows food and gasses into the

cell and waste products out of the cell

– “the bouncer”

Cell Structures

• Cytoplasm– A gelatin-like substance

inside the cell membrane– Medium for things to move

about in the cell

• Cytoskeleton– Scaffolding-like structure in

cytoplasm which helps cell keep its shape

• Organelles– Membrane bound structures

inside eukaryotic cells that helps the cell perform life processes

Cell Structures

• Nucleus– Organelle that directs

all cell activities – Contains instructions

for everything a cell does (within the DNA)

– “foreperson”

Cell Structures• Chloroplasts

– Organelles in plants and a few bacteria that help the organism make food

– Photosynthesis occurs here

• Mitochondria – Organelles in all eukaryotes

that release the energy from food and turn it into something the organism can use

– “powerhouse”

Cell Structures

• Ribosomes– Organelles that make proteins– Produced in the nucleus

• Endoplasmic Reticulum (ER)– Series of folded membranes from

the nucleus to the cell membrane– Moves materials around in a cell

• Two types of ER– Rough – ribosomes are attached– Smooth – no ribosomes attached

• Material movement and lipid processing

Cell Structures

• Golgi Bodies– Sort proteins and other cellular

substances and package them into membrane-bound structures called vesicles

– “post office”

• Vacuoles– Organelles that serve as

temporary storage for materials• Can be water, waste products,

food, etc.

– Vacuoles make up most of the volume of plant cells

Cell Structures

• Lysosomes– Organelles that

contain digestive chemicals that help break down food molecules, cell wastes, and worn-out cell parts

– “recycler”

From Cell to Organism

• Cell• Tissues

– Groups of similar cells working together on one job

• Ex: muscle tissue, nervous tissue

• Organ– Different types of tissues

working together • Ex: muscle, brain

From Cell to Organism

• Organ System– A group of organs working

together on a particular function• Ex: muscular system, nervous

system

• Organism – All of organ systems working

together to create a particular organism

Review Questions

1. Explain the important role of the nucleus in the life of a cell.

2. Compare and contrast the energy processing organelles.

3. Why are digestive enzymes in a cell enclosed in a membrane-bound organelle?

4. How are cells, tissues, organs and organ systems related?

5. How is the cell of a one-celled organism different from the cells in many-celled organisms?

6. What are some differences between plant and animal cell?

7. List 3 organelles and give their functions.

Early Microscopes

• Dutch reading glass maker put two lenses at ends of a tube (1500s)– Larger image

• Antonie van Leeuwenhoek (Dutch fabric merchant)– First simple microscope (p.

50 in book)

– Could magnify up to 270 times

Modern Microscopes

• Use lenses to bend light• A simple microscope has one lens

while a compound microscope (what we have here) has mulitple lenses – Ex: one lens at 10x – 10 times bigger

• Two lenses at 10x – 100 times bigger

• Stereomicroscopes have two eyepieces, which create a three-dimensional image

Electron Microscopes• Use a magnetic field inside a

vacuum to bend electronic beams– Scanning Electron

Microscope (SEM) bounce electrons off the sample to create a 3-D image

– Transmission Electron Microscope (TEM) send electrons through a sample to see internally

• Either way, electons then end up on a screen to produce an image (kind of like older TVs)

Cell Theory

• 1665, Robert Hooke looked at cork under a microscope– Made of little boxes he

named cells

• 1830s, Matthias Schleiden studied plant parts– Concluded all plants

are made of cells

Cell Theory

• Theodor Schwann looked at animal cells– Concluded all animals are

made up of cells

• Rudolf Virchow– Said that cells come from other

cells that already exist

Cell Theory

• All organisms are made up of one or more cells

• The cell is the basic unit of organization in organisms

• All cells come from pre-existing cells

Review Questions

1. Explain why the invention of the microscope was important in the study of cells.

2. What is stated in the cell theory?3. What is the difference between a simple

microscope and a compound microscope?4. What was Virchow’s contribution to the cell

theory?5. How do electron microscopes work?6. Why would it be better to look at living cells

rather than dead cells?

Cell Processes

• Passive Transport – the movement of substances through a cell membrane without the use of energy– Diffusion or Osmosis

• Active Transport – the movement of substances through the cell membrane using energy

• Endocytosis & Exocytosis – vesicles transport large materials into (endocytosis) and out of (exocytosis) the cell

Cell Processes• Photosynthesis

– The process plants and other organisms use to convert sunlight energy into chemical energy or sugars to be used as food

• Respiration– The process in which chemical

reactions break down food molecules into simpler substances and release stored energy

• Fermentation– Cells that do not have enough

oxygen for respiration use this process to release some of the stored energy in glucose molecules

Cell Processes

• Cell Division – process where one cell splits into two cells

• Mitosis – process in which the nucleus divides to form two identical nuclei– Four stages: Prophase, Metaphase, Anaphase, Telophase– Happens during growth of organism or during asexual

reproduction

• Meiosis – process in which the nucleus divides to form cells with half the genetic material of the original– Eight Stages: Prophase I, Metaphase I, Anaphase I, Telophase

I, Prophase II, Metaphase II, Anaphase II, Telophase II– Happens when an organism produces gametes (sex cells) for

sexual reproduction

Review Questions

1. What is active transport?

2. What are the two main types of passive transport?

3. How do cells get large materials out?

4. What is photosynthesis?

5. What is respiration?

6. What is mitosis and when does it happen?

7. What is meiosis and when does it happen?