Topic 1- Cell biology

Question 1

Eukaryote:

Answer 1

Animal and plant cells
* Cell membrane
* Cytoplasm
* Nucleus cotaining DNA

Question 2

Prokaryote:

Answer 2

Bacterial cells
* Cell wall
* Cell memrane
* Cytoplasm
* Single circular strand of DNA
* Pasmid (small loops od DNA)

Question 3

Permanent vacuole:

Answer 3

• Contains cell sap
• Foound within cytoplasm
• Improves cell’s rigidity

Question 4

Cell membrane:

Answer 4

• Controls what enters and leaves the cell

Question 5

Cell wall:

Answer 5

• Prevents cell from bursting when water enters by osmosis
• Provides strength to the cell

Question 6

Sperm cell:

Answer 6

Specialised to carry the male’s DNA to the egg for reproduction.
* Streamlined head and long tail- to aid swimming
* Many mitrochondria (where respiration happens)- supplies the energy to allow the cell to move

Question 7

Nerve cells:

Answer 7

Specialised to transmit electrical signals quickly from one place in the bioy to another
* The axon is long- enables impulses to be carried along long distances
* Many dendrites- branched connections can form with other nerve cells
* Nerve endings have many mitochondria- supplies the energy to make special transmitter chemicals called neurotrnasmitters. These allow the impulse to be passed from one cell to another.

Question 8

Muscle cells:
💪

Answer 8

Specialised to contract quickly to move bones or simply to squeeze, therefore causing moveement.
* Special proteins side over ecahother, causing the muscle to contract
* Lots of mitochondria- provide energy from respiration for contraction
* Stores glycogen- used in respiration by mitochondria

Question 9

Root hair cells:

Answer 9

Specialised to take up water by osmosis and mineral ions by active transport fro t he soil as they are found in thee tips of the roots.
* Have a large surface area due to root hair cells- more water can move in
* Large permaneent vacuole- affects speed of movement of water from soil to cell
* Mitochhondria- provide energy from respiration for the active transport of mineral ions into the root hair cell

Question 10

Xylem cells:

Answer 10

Specialised to transport water and mineral ions up the plant from the roots to the shoots.
* Lignin is deposited- causing the cells to die
* They become hollow and are joined end to end- forms a continuous tube so water and mineral ions can move through

Question 11

Phloem cells:

Answer 11

Specialised o carry the products of photosynthesis to all parts of the plant.
* Cell walls of each cell- form structures called sieve plates when they break down, allowing the movement of substances from cell to cell

Question 12

Cell differentaiation:

Answer 12

To become specialised, stem cells must undergo differentiation to form specialised cells. This invloves them accquiring different sub-cellular structures to enale it to carry out a certain function.
* In animals- most cells differentiate at an early stage, then lose this ability
* In plant cells- many cells retain the zability to differentiate hrough their life.

Question 13

Microscopy:
🔬

Answer 13

• The first microscpe was the light miscroscpe
• Light microscpes are used to view tissues, cells and large sub-cellular structures
• The electron microscope was then developed- allowing siienists to view deep inside sub-cellular structures, such as mitochondria, robosomes, chloroplasts and plamsids.
• Electron microscopes have a higher magnification than light

Question 14

Culturing microrganisms:
🧫

Answer 14

There are two ways to grow microoganisms in the lab:
1. In nutrient broth solution
2. On an agar plate
Making the plate:
* Hot sterilised agar jelly is poured into a sterile petri dish, which is left to cool and set
* Wire loops containing inoculating loops are dipped into a solution of the microorganism and are spread aver the agar evenly
* A lid is tapped on and the plate iss incubated for a few days so the microorganisms can grow.

Question 15

Culturing microorganisms- reasons for key steps:

Answer 15

• Petri dishes sterilised using a UV light- so it is not contaminated with other microorganisms (they will compete with desired bacteria for food and space)
• Inoculating loops must be sterilised by passing them through a flame- kills unwanted organisms
• The lid of the petri dish should be sealed with tape- stops airborne microorganisms from contaminating the culture
• Culture dish incubated at 25 degrees- this is the optimum temperature. At a higher temperature, the bacteria could be harmful to humans and any lower, colonies of bacteria would not be able to grow.

Question 16

How is genetic information stored in a prokaryotic cell?

Answer 16

• Chromosomal DNA
• Plasmid DNA

Question 17

What are plasmids?

Answer 17

• Small, circular loops of DNA that are found free in the cytoplasm and seperate from the main DNA.
• Carry genes that provide genetic advantages e.g. antibiotic reistance.

Question 18

What is a micrometre?

Answer 18

1 x10^-6

Question 19

What is a nanometre?

Answer 19

1x 10^-9

Question 20

What is the function of the nucleus?

Answer 20

• Controls the cell
• Stores genetic information

Question 21

What is the plant cell wall made out of?

Answer 21

Cellulose

Question 22

What is cell differentiation?

Answer 22

The process of which cells become specialised.

Question 23

Why is cell differentiation important?

Answer 23

• Allows for the production of different tissues and organs that perform various vital functions in the human body.

Question 24

At what point in the life cycle do animal cells differentiate?

Answer 24

Early in the life cycle.

Question 25

How long **plant cells** retain the **ability to differentiate?**

Answer 25

Throughout their **whole life cycle.**

Question 26

What is the purpose of **cell division** in **mature animals?**

Answer 26

**Repair and replacement** of cells

Question 27

What changes does a cell go through as it differentiates?

Answer 27

It becomes **specialised** through **acquisition** of different **sub-cellular structures** to enable a **specific function** to be **performed by the cell.**

Question 28

Define magnification.

Answer 28

The **number of times an mage appears bigger** compared to the **object's actual size.**

Question 29

Define **resolution.**

Answer 29

The **smallest distinguishable distance** between **two objects.**

Question 30

What are the **advantages** of **light microscopes?**

Answer 30

* Not expensive * Portable * Able to obseve both **dead and living** specimens

Question 31

What are the **disadvantages** of **light microscopes?**

Answer 31

Limited resolution

Question 32

What are the advantages of electron microscopes?

Answer 32

* Greater magnification * Greater reoluion

Question 33

How have **elctron microscopes** allowed **scientists** to develop a **deeper understaning of cells?**

Answer 33

* **Sub-cellular structures** to be observed in **detail.** * Scientists have developed **more accurate explanations** of how **cell structure relates to function.**

Question 34

What are **disadvantages** of **electron microscopes.**

Answer 34

* Expensive * Large, so less portabls * Require training to use * Only dead specimens can be observed

Question 35

Equation for calculating **magnification**.

Answer 35

Magnification = Image/real

Question 36

How do bacteria multiply?

Answer 36

Binary fission.

Question 37

How often do **bacteria multiply?**

Answer 37

**Once** every **20 minutes** if **nuterients** are available and the **temperature is suitable**

Question 38

State **2 ways** in which **bacteria** can be **grown.**

Answer 38

* Nuterient broth solution * Colonies on agar gel plate

Question 39

What **nutrients** make up a **nutrient broth solution?**

Answer 39

**All nutrients required for bacteria to grow** including **nitrogen** for **protein sythesis,** **carbohydrates** for **energy** and other minerals.

Question 40

What are **uncontaminated cultures** of **microorganisms** needed for?

Answer 40

Investigating **disinfectant** and **antibiotic action.**

Question 41

Describe the **preperation** of an **uncontaminated culture** using **aseptic technique.**

Answer 41

1) Usse **pre-sterilised plastic Petri dishes or** **sterilise glass petri dishes and agar gel** before using with an **autoclave.** 2) **Pour** the **sterilised agar gel** into the **petri dish** and give time for it to **set** 3) **Sterilise** the **inoculating loop** by passing it through a **bunsen burner flame.** 4) **Dip** the **inoculating loop** into the **solution** of **microorganisms** and make **streaks with the loop** on the **surface** of the **agar** 5) **Put** the **lid** on the **petri dish** and secure it with **tape.** Label accordingly then **turn** and **store upside down** 6) **Incubate** the **culture** for **48 hours at 25°C** in **school labratories**

Question 42

**Why** must **petri dishes** and **culture media** be **sterilised** before use?

Answer 42

To **kill any bacteria** already **present.**

Question 43

Why must **inoculating loops** be **sterilised** by passing them through a **Bunsen burner flame?**

Answer 43

To **kill any bacteria present** on the inoculating loop.

Question 44

Why must the **petri dish** be **secured with tape** and the **whole dish stored uppside down?**

Answer 44

* To **stop bacteria in the air contaminating the culture** * But the **lid is not fully sealed** to **prevent the growth of anaerobic bacteria** in a **lack of oxygen** * **Upside down-** to prevent **condensation** from **forming** and **dripping** down onto the **colonies.**

Question 45

Why are cultures incubated at 25°C in school labratories?

Answer 45

**Harmful pathogens** are less **likely to grow** at this **temperature.**

Question 46

**What** is the equation to calculate the **number of bacteria.**

Answer 46

**Number of bacteria at end of time period** = number of bacteria at beginning x 2^number of divisions in time period

Question 47

What are **chromosomes** made up of?

Answer 47

Chromrosmes **consist of DNA molecules combined with proteins.** They **contain genes** which provide the **instructions** for **protein synthesis.**

Question 48

What is a **gene?**

Answer 48

A **section of DNA** which **codes** for a **specific protein.**

Question 49

How many **chromosomes** are found in the **nucleus** of a **human body cell?**

Answer 49

46

Question 50

How many **chromosomes** are found in the **nucleus of gametes?**

Answer 50

23

Question 51

How are **chromosomes arranged** in the **nucleus** of a **human body cell.**

Answer 51

In **pairs**- there are **23 pairs**

Question 52

What are the **three main stages** of the **cell cycle?**

Answer 52

1) **DNA replication** and **number of sub-cellular structures increase** 2) **Mitosis** 3) **Division** of cell

Question 53

Why is **mitosis important?**

Answer 53

* Produces **identicall cells** which **all** have the **same genetic information.** * Produces **additional cells** for **growth and repair.**

Question 54

Describe the **first stage** of the cell cycle.

Answer 54

**THE LONGEST STAGE:** * **Cells grow** * **DNA replicate** * Number of **sub-cellular structures** increase e.g. mitochondria nad ribosomes

Question 55

Describe the **second stage** of the **cell cycle.**

Answer 55

**Each pair of chromsomes** is **pulled to each end of the cell,** the the **nucleus divides.**

Question 56

Describe the **third stage** of the **cell cycle.**

Answer 56

* The **cytoplasm** and **cell membrane divide** * **Two identical daughter cells** are produced

Question 57

What is a **stem cell?**

Answer 57

An **unspecialised cell** which is **capable** of **differentiating** into **other cell types** and of **self-renewal.**

Question 58

What is the **function** of **stem cells** in **embryos?**

Answer 58

* **Embryonic stem cells** can **replicate** themselves and **differentiate** into **many other types of cells.** * **Embryonic stem cells** may be able to **treat conditions** such as **paralysis** and **diabetes** by **dividing** to **replace damaged cells.**

Question 59

What is the **function** of **stem cells** in **adult bone marrow?**

Answer 59

* **Adult stem cells** can **differentiate** into **several cell types** to **replace dead or damaged tissues.** * For example, **bone marrow stem cells** can form **many different types of blood cell.**

Question 60

What is the **function** of stem cell in **plant meristems?**

Answer 60

* **Meristem** cells **retain** the **ability** to **differentiate** into **any type** of **plant cell** throughout their **lifespan** * They can **differentiate** into **any cell** which is **required by the plant.**