Bio- Chapter 2

What are Cells?

Chapter 2; U1AOS1

2A

Cells as the Basis of Life

LI:

To understand the characteristics of living things,

and compare prokaryotes and eukaryotes.

SC: I can

- Explain the characteristics of living things

- Distinguish between prokaryotes and eukaryotes

What makes something

a living thing?

Characteristics of Living Things

1. Movement - can it move on its own?

2. Respiration - can it extract nutrients through aerobic/anaerobic respiration?

3. Sensitivity - can it react to stimuli?

4. Growth - does it grow larger over time?

5. Reproduction - can it produce new living things sexually or asexually?

6. Equilibrium - can it maintain homeostasis (stable internal environment)?

7. Excretion - does it produce waste products that need to be removed?

8. Nutrition - can it extract nutrients autotrophically or heterotrophically?

What are cells?

In addition to the ‘Mrs Green’ characteristics of living things, all

organisms must function according to Cell Theory, which states:

● All living things are composed of cells

● Cells are the smallest and most basic unit of life

● All cells come from pre-existing cells

Robert Hooke invented the compound microscope and illumination

system, and in 1665 published Micrographia detailing his discovery

that living things were made of “cells”, named so as they reminded

him of box-like rooms in which monks lived in monasteries.

Categorising Life

Living things can be categorised based on their cellular structures as either

eukaryotic or prokaryotic organisms, and further classified into domains

and kingdoms.

Prokaryotes & Eukaryotes

The key feature separating eukaryotes and a prokaryotes is that a prokaryote lacks a membrane-bound

nucleus. On average, prokaryotic cells are also typically 10x smaller than eukaryotic cells.

The general features of a prokaryotic cell are:

● Capsule: sticky coating

● Cell envelope: cell wall & plasma membrane

● Nucleoid: contains large, free-floating circular DNA

● Ribosomes: synthesises protein

● Plasmids: a smaller, circular loop of DNA separate

from a chromosome, often in bacteria

● Cytosol: the aqueous fluid that surrounds the

organelles inside a cell

● Flagella: for propulsion (movement)

● Pilli: attachment structure

Comparing Prokaryotes & Eukaryotes

2B

Organelles

LI:

To develop an understanding of organelles and

compare organelles found in plant and animal

cells.

SC: I can

- Explain the structure and function of organelles

- Distinguish between plant and animal cells

Organelles

An organelle can be defined

as any specialised structure

that performs a specific

function in the cell to keep it

functioning.

A cell has many differently

shaped organelles that work

together to increase the

efficiency of the cell.

Main Function:

Synthesis & Processing

of Proteins and Lipids

Nucleus

Found: Eukaryotic Cells (Plants & Animals)

Membrane Bound: Yes

Structure

Separated from the rest of the cell by a nuclear envelope,

the nucleus has a double membrane with pores that

allow substances in/out of the nucleus. The nucleolus is

inside the nucleus, and is a region of the cell’s DNA on

which ribosomal RNA (rRNA) ribosomes are being made.

Function

As the control centre of the cell, the nucleus confines the

genetic information (DNA) of the cell. DNA is tightly

wound around proteins to form chromosomes, and the

nucleus coordinates the cell’s activities by coding for

specific proteins that complete a specific function at a

specific time.

Ribosome

Found: All cells (Prokaryotic & Eukaryotic)

Membrane Bound: No

Structure

● 60% ribosomal RNA (rRNA) and 40% protein

● Float freely in the cell or attached to the rough ER.

Function

The two subunits lock together around the messenger

RNA (mRNA) - a single stranded genetic code from the

nucleus - and convert it into a chain of amino acids to

form a functional protein.

Endoplasmic Reticulum (ER)

Found: Eukaryotic Cells (Plants & Animals)

Membrane Bound: Yes

Structure

A network of flattened membranous channels

- Rough ER: coated with ribosomes

- Smooth ER: NOT coated with ribosomes

Function

The ER transports materials within the cell and is:

- Rough ER: Responsible for protein modification

- Smooth ER: Responsible for lipid production

Lysosome

Found: Eukaryotic Cells (Plants & Animals)

Membrane Bound: Yes

Structure

Fluid-filled sacs containing many digestive

enzymes.

Function

Lysosomes are specialised vesicles that are

responsible for digesting (breaking down)

cell waste and toxins.

Golgi Apparatus

Found: Eukaryotic Cells (Plants & Animals)

Membrane Bound: Yes

Structure

A stack of flattened membrane-bound sacs

(cisternae).

Function

Proteins made in the rough ER move to the golgi

apparatus in transition vesicles. The golgi

apparatus then modifies and packages proteins

into secretory vesicles for export out of the cell.

Main Function:

Energy Transformations

Mitochondria

Found: Eukaryotic Cells (Plants & Animals)

Membrane Bound: Yes

Structure

Small, oval-shaped organelles with their own DNA and

ribosomes. Each mitochondrion consists of:

● An outer membrane

● A highly folded inner membrane (cristae)

● A low-volume intermembrane space (mitochondrial matrix)

The number of mitochondria in a cell is correlated to its energy

requirement (ie active cell = many mitochondria).

Function

The mitochondria is the site of aerobic cellular respiration, where

glucose is broken into ATP (energy) to be used within the cell to

perform functions like movement, reproduction or communication.

Chloroplast

Found: Eukaryotic Cells (Plants/Algae Only)

Membrane Bound: Yes

Structure

Contain a double membrane, filled with a fluid

substance (stroma) and stacks of flattened sac-like

structures called thylakoids (a granum) that contain

chlorophyll - a green pigment - to absorb light energy.

Function

Chloroplasts are the site of photosynthesis, where light

energy (from the sun) is transformed into chemical

energy (glucose/sugar) to fuel cellular respiration, to

build cell walls and carry out metabolic reactions.

Main Function:

Storage & Cell Structure

Vacuole

Found: Eukaryotic Cells (Plants & Animals)

Membrane Bound: Yes

Structure

● A fluid-filled space surrounded by a tonoplast

membrane separating the vacuole and cytosol

● One large vacuole in plant cells (80-90% cell)

● Many or no smaller vacuoles in animal cells

Function

Used for sugar, minerals, proteins and water storage,

as well as helping to maintain plant cell structure.

Vesicle

Found: Eukaryotic Cells (Plants & Animals)

Membrane Bound: Yes

Function

A small membrane-bound sac that transports

substances into (endocytosis) or out of (exocytosis)

a cell, or stores substances within a cell.

Cell Wall

Found: Eukaryotic Cells (Plants Only)

Membrane Bound: No

Structure

Made of cellulose, a complex carbohydrate molecule

that allows cells to swell following water intake

without bursting.

Function

A sturdy border outside the plasma membrane that

prevents overexpansion and provides protection,

shape, strength and structure for plant cells. Water

and dissolved substances can pass freely through it.

Cell Membrane

Found: Eukaryotic Cells (Plants & Animals)

Membrane Bound: No

Structure

Composed of a phospholipid bilayer

(more on this in Chapter 3!), with embedded

proteins, carbohydrates and cholesterol.

Function

A semi-permeable barrier that separates

individual cells and controls the entry and

exit of substances from one cell to another.

Cytoskeleton

Found: Eukaryotic Cells (Plants & Animals)

Membrane Bound: No

Structure

Composed of a large network of microtubules

(hollow cylindrical tubes) and microfilaments

(solid contractile proteins) that start at the

nucleus and reach out to the plasma membrane.

Function

The cytoskeleton is critical for supplying support

and strength to maintain the cell’s shape,

transporting vesicles and organelles within a cell,

and enabling some cell mobility.

Cell Appendages

Cilia & Flagella

Cilia

Cilia are short hair structures which allow them to

move around.

● Several short appendages.

● Usually lines the cell.

Flagella

Flagella are long whip like structures which allows

them to move across their environment

(flagellum for only one).

● 1-2 long appendages.

● Tail-like appendage.

Cilia and flagella are not organelles, but whip-like structures located on the outside of eukaryotic cells

which allow them to move, or move fluids across the cell surface. They contain protein fibres that move

relative to each other to allow the structure to ‘wave’.

Cytosol & Cytoplasm

Cytosol & Cytoplasm

The cytosol and cytoplasm are not

organelles, but are important parts of the

cell’s anatomy.

● The cytosol is the aqueous fluid that

surrounds the organelles inside a cell.

● The cytoplasm includes the cytosol

and organelles inside the plasma

membrane, except the nucleus.

2C Cell Size & Shape

LI:

To understand the importance of surface

area:volume ratio (SA:V) for cell efficiency

SC: I can

- explain what the SA:V ratio is

- list ways to increase the SA:V ratio

The Dilemma:

It’s 8pm, and you have been studying so hard you

forgot dinner! You have all the ingredients for a

potato curry, but potatoes take forever to cook. How

can you speed up the cooking time of the potatoes?

Why are cells so small?

Cells are microscopic, and unable

to be seen by the naked eye.

However, all cells must maintain homeostasis

and complete multiple functions that require

an exchange of materials between the cell

and its environment.

So, there is a delicate balance between the

size of the cell and its ability to gain

requirements and remove enough wastes

across its plasma membrane to sustain life.

We can measure the exchange of materials

into and out of the cell using the

surface area: volume (SA:V) ratio