Lesson 1 : Cell Biology

Cells

Basic unit of life

Eukaryotes

Organisms with cells that contain membrane bound organelles/ a nucleus

Prokaryotes

Organisms made up of cells that do not contain membrane bound organelles/ a nucleus

Sub-cellular structures in an animal cell

1. Nucleus

2. Cytoplasm

3. Cell membrane

4. Mitochondria

5. Ribosomes

Sub-cellular structures in a plant cell

1. Nucleus

2. Cytoplasm

3. Cell membrane

4. Mitochondria

5. Ribosomes

6. Chloroplasts

7. Cell wall

8. Permanent vacuole

Sub cellular structures in a bacterium

1. Cytoplasm

2. Cell membrane

3. Cell wall

4. Slime capsule

5. Single DNA loop

6. Plasmids

7. Flagella/Flagellum (on some occasions)

Function of Nucleus

Directs all the cells activities; contains the cells DNA

Fiction of Mitochondria

Site if aerobic respiration

Function of cytoplasm

Gel-like substance where chemical reactions take place

Function of cell membrane

regulates what enters and leaves the cell (partially/selectivley permeable)

Function of ribosomes

Site of protien synthesis

Function of cell wall

Strengthens and supports the cell

Function of permanent vacuole

fills with cell sap to help keep the cell turgid

Function of chloroplasts

Site of photosynthesis

Function of plasmids

Carries extra genes giving bacteria useful traits

Eg: Antibiotic resistance

What is the function of a sperm cell?

To travel to and fertilise the egg

How are sperm cells specialised for their function?

1. Flagellum - allows sperm to swim to egg

2. Streamlined head - helps it swim faster and more efficiently

3. Lots of mitochondria - to release energy required for swimming

4. Contains digestive enzymes at the tip to help break down outer layer of egg cell

What is the function of a nerve cell?

To carry electrical impulses from one part of the body to another

How are nerve cells specialised for their function?

1. Long axon - allows electrical impulses to travel long distances without interruption

2. Myelin sheath - insulates cell and speeds up transmission of impulses

What is the function of a muscle cell?

To contract quickly to bring about movement

How are muscle cells specialised for their function?

1. Mitochondria - lots of mitochondria release energy

2. Stored glycogen - can be broken down into glucose during respiration

3. Special protein filaments - can slide over each other causing muscle cell to relax and contract

What is the function of a root hair cell?

Absorbs water and mineral ions from the soil.

How are root hair cells specialised for their function?

1. Long hair like extension - increases surface area for faster absorption

2. Thin cell wall - shortens diffusion distance

3. Lots of mitochondria - release energy required for active transport

What is the function of xylem cells?

To transport water and mineral ions up the plant

How are xylem cells specialised for their function?

1. Dead cells with no end walls - forms hollow, continuous tube so water can flow easily

2. Cells wall reinforced by lignin - supports plant and prevents tubes from collapsing

What is the function of phloem cells?

Transport dissolved sugars up and down plant (translocation)

How are phloem cells specialised for their function?

1. Sieve plates - end walls have pores that allows sugars to move freely through tube

2. Very few sub-cellular structures - more space for food to flow

3. Companion cells - have lots of mitochondria that provide energy required for translocation

light microscope

uses light and lenses to enlarge an image of an object

Electron microscope

Uses electrons to form an image

How has the electron microscope increased understanding of sub cellular structures?

An electron microscope has a much higher magnification and resolving power than a light microscope, meaning that cells can be studied in much finer detail. This has enabled biologists to see and understand many more sub-cellular structures

Formula for magnification

Image size/real size (I/AM)

Magnification

the ratio of an object's image size to its real size

Resolution

The ability to distinguish between two points on an image

Parts of a light microscope

1. Eyepiece

2. Objective lenses

3. Stage

4. Light

5. Coarse adjustment knob (big)

6. Fine adjustment knob (small)

How do bacteria reproduce?

asexually through binary fission (at a suitable temperature they can double in number every 20 minutes)

Describe how you should prepare an uncontaminated bacterial culture using aseptic technique

1. Sterilise Petri dish and agar to kill any unwanted microorganisms and prevent contamination

2. Sterilise inoculating loop by passing it through a Bunsen burner flame

3. Transfer bacteria onto the dish using inoculating loop

4. After transferring bacteria, attach lid of Petri dish using adhesive tape. This stops lid from falling off and unwanted microorganisms entering

5. Place agar plate upside down in an incubator. This stops moisture dripping down onto bacteria and disrupting the colonies

6. In school laboratories bacteria are incubated at 25C in order to reduce the chance of harmful bacteria growing

Differentiation

The process of cells specialising for their function

Stem cell

an undifferentiated cell of an organism that is capable of giving rise to many more cells of the same type, from which certain other cells can arise from differentiation

Types of stem cells

1. Embryonic stem cells

2. Adult stem cells

3. Meristem tissue

Adult stem cells

Stem cells that can only differentiate into specific types of cells

Where are adult stem cells found?

Bone marrow, liver, skin, and pancreas tissue

Embryonic stem cells

Stem cells that can differentiate into most types of cells

Where are embryonic stem cells found?

In early human embryos

Chromosomes

Coiled up lengths of DNA molecule

electron vs light (compound) microscope

Electron:

1. Higher resolution

2. Higher magnification

3. Needs dead specimen

Light:

1. Cheaper

2. Easy to use

Cell cycle

1. Interphase (Grow and increase number of sub-cellular structures and DNA replication )

2. Mitosis (one set of chromosomes is pulled to each end of the cell and the nucleus divides)

3. Cytokinesis (Cell membrane splits)

Mitosis

Cell division in which 2 daughter cells produced are genetically identical to parent cell

Stages of mitosis

prophase, metaphase, anaphase, telophase

Diffusion

Net movement of particles from an area of high concentration to an area of low concentration

Why do multicellular organisms need exchange surfaces?

They have a small SA to volume ratio

How are the lungs adapted for gas exchange?

1. Millions of alveoli - increase SA

2. Thin walls (one cell thick) - very short diffusion distance

3. Excellent blood supply - maintains steep concentration gradient

How is the small intestine adapted for gas exchange?

1. Villi and microvilli - massively increase SA

2. Lining is one cell thick - short diffusion pathway

3. Rich capillary network - maintains steep concentration gradient by quickly removing nutrients

How are gills in fish adapted for gas exchange?

1. Gill filaments and lamellae- huge SA

2. Thin surface membrane - short diffusion pathway

3. Counter current flow - blood and water flow in opposite directions to maintain a steep concentration gradient

How are leaves in plants adapted for gas exchange?

1. Flat wide shape - large surface area to volume ratio

2. Stomata - let gas in and out

3. Spongy mesophyll - let gases move and diffuse easily inside

4. Very thin - creates short diffusion distance to cells

How are plant roots (root hair cells) adapted for gas exchange?

1. Root hair cells - long extension creates large surface area

2. Thin cell walls - short diffusion distance

3. Lots of mitochondria - release energy required for active transport

Osmosis

Movement of water particles from a dilute solution to a concentrated solution across a partially permeable membrane.

Active transport

Movement of particles against the concentration gradient using energy.

examples of active transport

1. Absorption of mineral ions into plant root hairs

2. Absorption of sugar molecules from lower concentrations in the gut into the blood which has a higher sugar concentration.

Factors affecting cell transport

1. Surface area to volume ratio

2. Temperature

3. Concentration

4. Distance

5. Constant concentration gradient

6. Steep concentration gradient