B1: Cell structure and transport

Examples of eukaryotes

• Plants

• Animals

Eukaryotic cells

Contain genetic material (DNA) enclosed in a nucleus

Features of eukaryotic cells (animal + plant cells)

1. Cell membrane

2. Cytoplasm

3. Genetic material enclosed in a nucleus

Examples of prokaryotes

Bacteria

Prokaryotic cells

Genetic material (DNA) isn’t enclosed in a nucleus

Are prokaryotic cells bigger or smaller than eukaryotic cells?

Much smaller

Features of prokaryotic cells

1. Cytoplasm

2. Cell membrane

3. Cell wall

4. Single DNA loop

5. + may be 1 or more small rings of DNA (plasmids)

Plasmids

Small rings of DNA in prokaryotic (bacterial) cells

How is genetic material found in prokaryotic cells?

Single loop of DNA

• + 1 or more plasmids

• GM not enclosed in a nucleus

Express these units in terms of a metre

1. cm- centimetre

2. mm- millimetre

3. μm- micrometre

4. nm- nanometre

1. 1 cm = 1 × 10^-2 m (1/100 of a m)

2. 1 mm = 1 × 10^-3 m (1/1 000 of a m)

3. 1 μm = 1 × 10^-6 m (1/1 000 000 of a m)

4. 1 nm = 1 × 10^-9 m (1/1 000 000 000 of a m)

Size of a typical human cell

10-20 μm

1 order of magnitude

10x

2 orders of magnitude

100x

How much greater is every order of magnitude compared to the one before?

10x greater

How can you find out the order of magnitude?

Count the no. of 0’s

1. 10x = 1 OoM

2. 100x = 2 OoM

3. 1000x = 3 OoM

Parts of a basic animal cell

1. Nucleus

2. Cytoplasm

3. Cell membrane

4. Mitochondria

5. Ribosomes

Nucleus

Encloses genetic material

Cytoplasm

Watery solution where chemical reactions take place

• Eg 1st stage of respiration

Cell membrane

Controls the molecules that can enter + leave the cell

Mitochondria

Site of aerobic respiration

Ribosomes

Site of protein synthesis

Can ribosomes be viewed with a light microscope?

No- electron microscope needed

Parts of a plant cell

Same as animal cell + 3 extra

1. Nucleus

2. Cytoplasm

3. Cell membrane

4. Mitochondria

5. Ribosomes

6. Chloroplasts

7. Cell wall

8. Permanent vacuole

Do plant and animal cells have a regular shape?

1. PC- regular shape

2. AC- can change shape easily

Chloroplasts

Contain chlorophyll + site of PS

What are plant cell walls made of?

Cellulose

Cell wall

Strengthens the cell

• Made of cellulose

Algae

Simple aquatic forms of plant life

What is the vacuole filled with?

A fluid- cell sap

Vacuole

• Packed with cell sap

• Helps give plamt cell its shape

Example of specialised animal cells

1. Sperm cells

2. Nerve cells

3. Muscle cells

4. RBC

Are most animal + plant cells specialised or unspecialized?

Specialised

What does it mean if a cell is specialised?

Cell has adaptations that help then carry out their particular function

Differentiation

When cells become specialised

Job of a sperm cell

Fertilisation- join with an ovum (egg cell)

During fertilisation what happens in terms of genetic info?

Genetic info of ovum + sperm combine

Adaptations of sperm cells

1. Contain only ½ the genetic info of a normal adult cell

2. Long tail + streamlined- helps swim to ovum

3. Packed full of mitochondria- provide energy needed for swimming

4. Contain enzymes- allow them to digest their way thru the outer layer of the ovum

Job of a nerve cell

Send electrical impulses around the body

Adaptations of a nerve cell

1. Long axon- carries EI from one part of the body to another

2. Myelin insulates the axon- speeds up transmission of nerve impulses

3. Synapses at end of axon- allow impulses to pass from 1 nerve cell to another

4. Dendrites on cell body- increase SA → other NC can connect easier

Synapses

Junctions that allow an impulse to pass from 1 nerve cell to another

What can muscles cells do?

Contract (get shorter)

What allows muscle cells to contract?

Contain protein fibres that can change their length

What happens when a muscle cell contracts?

Protein fibres get short → decreases length of MC

Adaptations of a muscle cell

1. Contain special protein fibres- can get shorter so MC contracts

2. Packed full of mitochondria- provides lots of energy for muscle contraction

3. Store glycogen- broken down + used in cellular respiration by mitochondria to transfer energy needed for fibres to contract

Do muscle cells work alone or in groups?

MC work tog to form muscle tissue

What happens as an animal cell differentiates to form a specialised cell?

It gets diff subcellular structures to enable it to carry out a certain function

Examples of specialised plant cells

1. Root hair cells

2. Xylem cells

3. Phloem cells

Structures present in a plant cell, but not animal cell

1. Chloroplasts

2. Cellulose cell wall

3. Permanent vacuole

Role of root hair cell

Helps plant cell take up water + MI more efficiently

What do hairs covering roots do?

Increase SA of root → so it can absorb water + dissolved MI more effectively

Adaptations of root hair cells

1. Root hair- increases SA of root → root can absorb water + dissolved MI more effectively

2. No chloroplasts- they are underground (no light), can’t carry out PS

3. Lots of mitochondria- transfer lots energy needed for AT of MI

4. Large permanent vacuole- speeds up movement of water by osmosis from the soil across the RHC

Why do root hair cells not have chloroplasts

• Chloroplasts contain chlorophyll- site of PS

• PS needs energy from light

• RHC = underground → no light → no PS

Where are xylem found?

Plant stem

Role of xylem

Form tubes that carry water + dissolved MI from roots to leaves

Adaptations of xylem cells

1. V thick walls containing lignin- provides support to the plant

2. End walls betw cells have broken down- cell forms a long tube → easier for water + dissolved MI

3. No internal structures (nucleus, cytoplasm, vacuole, chloroplasts)- easier for water + MI to flow

What causes xylem cells to die?

Lignin

Role of phloem cells

Phloem tubes carry dissolved sugars up + down the plant

How many diff types of cells does phloem consist of?

2

• Phloem vessel cells + companion cell

Phloem vessel cells

No nucleus + limited cytoplasm

Adaptations of phloem cells

1. PVC have sieve plates + no nucleus- allow dissolved sugars to. move thru the cell interior

2. Mitochondria in CC- provide energy to PVC

Sieve plates

Pores on the end walls of PVC

Why do phloem vessel cells need a companion cell?

PVC have limited cytoplasm = don’t have many mitochondria

How is a companion cell connected to a PVC?

Pores

Role of red blood cells

Transport O2 needed for AR in body cells

Adaptations of RBC

1. Biconcave shape- high SA:V → increases diffusion.

2. Lots of haemoglobin- binds O2

3. No nucleus- more space for haemoglobin to bind O2

4. Thin membrane- short diffusion pathway

What can substances do via diffusion?

Move into + out of cells across cell membranes

Diffusion

The spreading out of particles, resulting in a net movement from an area of higher conc to an area of lower conc

• Down a CG → no energy needed

Molecules that move in + out of cells via diffusion

1. Oxygen (in gas exchange)

2. Carbon dioxide (in GE)

3. Urea

What do cells need oxygen for?

Generate energy by respiration

• Carried out by mitochondria

Are cells surrounded by a high or low conc of oxygen and why?

High O₂ conc

• O₂ transported in BS from lungs

How does oxygen move in and out of cells via diffusion?

1. Start: higher O₂ conc out cells, lower conc inside

2. O₂ molecules move into the cell by diffusion- from an area of higher conc to an area of lower conc

3. O₂ then used to generate energy in respiration

   • Produces waste gas CO₂

What waste gas is produced in respiration?

Carbon dioxide

How does carbon dioxide move out of cells?

1. Start: higher conc of CO₂ inside cell, than outside

2. CO₂ moves out of the cell by diffusion

Urea

Waste product produced inside cells

How does urea move out of cells by diffusion?

1. Diffuses out of cells into blood plasma

2. Excreted by kidneys

How is urea excreted?

By kidneys

Factors affecting rate of diffusion

1. Conc gradient- difference in concs

2. Temperature

3. SA of the membrane

Factors increasing rate of diffusion (faster)

1. Greater CG

2. Higher temp

3. Larger SA of cell membrane

Why is the rate of diffusion increased at a higher temp?

• Particles have more KE

• So are moving faster

What molecule can move across cell membranes via osmosis?

Water

Osmosis

Diffusion of water from a dilute solution to a concentrated solution thru a partially permeable membrane

Do dilute and concentrated solutions have a high or low water conc?

• Dilute: high

• Concentrated: low

Partially permeable membrane

Only allow some molecules to pass thru

Is the cytoplasm of cells a relatively dilute or concentrated solution?

Concentrated

• Contains low water conc

What happens if you place an animal cell in water?

• Water moves by osmosis from outside the cell to inside the cell

• Causes it to expand

What happens when water moves into an animal cell?

Expands or bursts

What happens if you place an animal cell in a v concentrated solution?

• Water moves out of the cell by osmosis

• Cell will shrink

What happens if you place a plant cell in water?

• Water moves into the cell by osmosis

• Cell expands

Will a plant cell burst when water moves in?

No

• Cell wall prevents plant cell from bursting

• Cell becomes swollen (turgid)

What does the cell wall prevent in plant cells?

Cell from bursting

What happens if you place a plant cell in a concentrated solution?

• Water moves out of the cell by osmosis

• Cell shrinks (becomes flaccid)

1. Isotonic

2. Hypertonic

3. Hypotonic

Conc of solutes in the solution outside the cell is the … as internal conc

1. Same

2. Higher

3. Lower

How do plants rely on osmosis for support?

1. Water moves into plant cells by osmosis

2. Vacuole swells → pushes cytoplasm against cell wall

3. Turgor- pressure builds up until no more water can enter the cell

4. Pressure makes PC rigid → keeps stem + leaves upright

Why is osmosis important in plant cells?

Maintain turgor

Active transport

Moves substances from a more dilute solution to a more concentrated solution, against a CG

• Requires energy from respiration

What does AT require and where does it come from?

Energy from respiration

Diffusion vs active transport

Diffusion

1. Particles move down the CG

2. Doesn’t need energy from respiration

AT

1. Particles move against the CG

2. Needs energy from respiration

Where does active transport occur in humans?

Cells lining small intestine

Lumen

Cavity of small intestine where food is digested

Why is active transport needed in the small intestine?

Conc of sugars in lumen is lower than conc of sugars inside the cell

• → sugars can’t diffuse into the cell