2.6Unit 2: Cells, Development, Biodiversity and Conservation

SNAB Resources from Plants — IAL Edexcel Modular Revision Notes & Topical Questions

10 min read 13 parts Lesson 8 of 8 1 quiz

📚 IAL Edexcel Modular Hub / Topical Revision

0%read

Lesson summary

2.6 Resources from Plants — IAL EDEXCEL MODULAR notes: Describe plant cell and stem structure, the roles of starch, cellulose, water and ions, the practicals on fibres and antimicrobial plants, drug testing and sustainability.Cell wall — it lies outside the cell membrane and prov…

Middle lamella
Plasmodesmata
Chloroplast
Amyloplast
Xylem vessels
Sclerenchyma fibres

Part 1 of 11Plant cell structure

Plant cell structure

Cell wall

Cell wall it lies outside the cell membrane and provides support through the polysaccharide cellulose.

Middle lamella

Middle lamella it is the outermost layer that glues adjacent plant cells together and gives stability.

Plasmodesmata

Plasmodesmata narrow threads of cytoplasm lined with membrane that connect neighbouring cells for transport and communication.

Pits

Pits very thin regions of the cell wall, lined up in pairs between adjacent cells, that help transport.

Chloroplast

Chloroplast it is larger than a mitochondrion, with a double membrane, and is the site of photosynthesis.
Thylakoids containing chlorophyll stack into grana joined by lamellae, and parts of photosynthesis occur in thylakoid membranes and the stroma.
Circular DNA and ribosomes make proteins for chloroplast replication and photosynthesis.

Amyloplast

Amyloplast a small membrane-bound organelle that stores starch granules and converts them back to glucose when needed.

Vacuole

Vacuole a sac of cell sap (water, minerals, waste, enzymes) surrounded by the selectively permeable tonoplast.

It keeps cells turgid so the plant does not wilt, and isolates unwanted chemicals.

Part 2 of 11Xylem and sclerenchyma

Xylem vessels

Xylem vessels they transport water and dissolved minerals and give structural support.
Lignin in the walls lets them withstand the pressure of the moving water column.
They are long hollow tubes of dead cells, with no cytoplasm or organelles to slow flow.
Unlignified pits allow lateral movement of water and minerals between vessels.

Sclerenchyma fibres

Sclerenchyma fibres they provide support only, as bundles of dead, lignified cells.
They form long tubes with end walls present and no pits.
Their walls contain more cellulose than other plant cells.

Part 3 of 11Phloem and vascular bundles

Phloem

Phloem it transports organic compounds (assimilates), mainly sucrose,
- from sources such as leaves to sinks such as roots, a process called translocation.
Transport is in both directions as sap, and phloem has no support function.
Mature phloem contains living cells, unlike xylem.

Sieve tube elements

Sieve tube elements main conducting cells that line up end to end to form a continuous tube.
They have no lignin and have sieve plates.

Companion cells

Companion cells each sieve tube element has one, containing a nucleus and cytoplasm.
They control the metabolism of the sieve tube element and load and unload sugars.

Other phloem cells

Other phloem cells parenchyma for storage and fibres for strengthening.

Vascular bundle

Vascular bundle xylem lies towards the middle of a stem and phloem nearer the outside, with sclerenchyma fibres giving extra support.

Part 4 of 11Water and inorganic ions

Water

Water it is needed for photosynthesis, transports minerals, keeps cells turgid by vacuole pressure and regulates temperature so enzymes work optimally.

Magnesium ions

Magnesium ions needed to make chlorophyll, which gives the green colour and is essential for photosynthesis.

Nitrate ions

Nitrate ions needed to make DNA, proteins and chlorophyll, for growth and for fruit and seeds.
- (including enzymes)

Calcium ions

Calcium ions needed for cell wall components and for proper growth.

Deficiency symptoms

Deficiency symptoms yellow leaves and stunted growth.

Uptake

Uptake ions and water enter through root hairs and travel up the stem in xylem.

Deficiency practical

Deficiency practical nine seedlings of the same age and plant are suspended in nutrient broths with high, medium or low calcium.
Roots dip into the broth and the tubes are covered in foil to keep light off the broth.
After a few days each seedling is blotted dry and the change in mass is found, giving a mean for each broth, and physical differences are noted.
A variation omits one mineral completely, with a control containing all minerals and another containing none.

Part 5 of 11Starch and cellulose

Starch and cellulose

Starch

Starch the plant storage polysaccharide kept as granules in plastids such as chloroplasts and amyloplasts.
Amylose (10–30% of starch) is an unbranched helix of alpha-glucose with 1,4 bonds, compact and resistant to digestion.
Amylopectin (70–90%) has 1,4 and 1,6 bonds, giving branches with many terminal glucose molecules for rapid hydrolysis.
Starch is compact and insoluble, so it has no osmotic effect, unlike glucose, which would draw water into cells.

Cellulose

Cellulose a polymer of beta-glucose joined by 1,4 glycosidic bonds.

Each beta-glucose is rotated 180° relative to the next to form the 1,4 bond.
Many hydrogen bonds between parallel chains form microfibrils with great strength.

Cell wall function

Cell wall function high tensile strength lets walls withstand turgor pressure.
Cellulose fibres and other molecules such as lignin form a matrix that strengthens the wall.

Part 6 of 11Plant fibres and tensile strength

Plant fibres

Plant fibres sclerenchyma fibres and xylem vessels are long hollow cells whose contents died, often because lignification stops substances entering or leaving.
Their strength is exploited in rope and fabrics such as cotton and hemp.
Strength results from mesh-like cellulose microfibrils and a thick secondary cell wall, often containing lignin, produced by secondary thickening.

Tensile strength

Tensile strength the maximum load a fibre can carry before breaking.

Plant fibres and tensile strength

Attach a fibre to a clamp on a retort stand and hang a weight on the other end.

Add weights one at a time until the fibre breaks and record the mass at which it broke.

Repeat with more samples of the same fibre and calculate the mean.

Control
- the fibres must be the same length and all other variables kept constant.

Part 7 of 11Practical: identifying tissue types in stems

Cut a very thin cross-section of the stem with a scalpel.

Stain it in a dish for one minute, for example with toluidine blue O (TBO).

Rinse the section in water and mount it on a slide.

Lower the coverslip slowly from one side to avoid air bubbles that could be mistaken for tissues.

View under the microscope and make a labelled drawing of the positions of the xylem vessels, phloem sieve tubes and sclerenchyma fibres.

TBO result
- xylem and sclerenchyma fibres appear blue-green and phloem appears pinkish purple.

Part 8 of 11Development of drug testing

1Clinical trials

Clinical trials new drugs are tested for effectiveness and side effects before they are sold.

2Digitalis soup

William Withering (1700s) treated dropsy with different concentrations of foxglove extract containing digitalis, which is poisonous.
He experimented on patients to find the most effective concentration that did not poison them.

3Modern testing

Modern testing drugs are modelled on computers, tested on human tissue in the laboratory, then on animals, then in clinical trials.

Phase	Subjects	Purpose
1	Small group of healthy people	How the body reacts, side effects and correct dose
2	Larger group of patients	Effectiveness of the drug
3	Large group of patients split into two groups	Compare the new drug with the existing drug

1Placebo

Placebo a tablet identical to the drug with no active ingredient, usually used in phase 2, with patients not told which they receive.
It shows whether the drug really works, because some patients improve through belief (placebo effect).

2Double blind

Double blind neither patient nor doctor knows who has the drug, which removes bias from attitudes (phases 2 and 3).

Part 9 of 11Antimicrobial properties of plants

1Bacterial growth conditions

Bacterial growth conditions nutrients, oxygen for aerobes and a suitable temperature and pH for enzymes.

2Antimicrobial

Antimicrobial kills microbes or prevents their growth.

Spread bacteria from a broth over an agar plate with a sterile pipette and plastic spreader, opening the lid as little as possible.

Dry and finely grind plant tissue, soak it in ethanol to extract antimicrobial substances and filter it.

Dip equal-sized discs of sterile absorbent paper in each extract with sterile forceps for the same time.

Dip a control disc in ethanol only.

Space the discs on the plate, tape the lid, invert the plate and incubate at 25 °C for 24–48 hours.

Analysis

Analysis the clear zone is the area around a disc where bacteria cannot grow.
A larger clear zone means more effective antimicrobial action.
Measure the diameter to the nearest mm and calculate area as πr² using the radius, repeating at least three times for a mean.

Aseptic technique

Aseptic technique it prevents contamination of the culture.
Keep windows and doors closed and disinfect surfaces and utensils.
Use sterile equipment and discard plastic instruments afterwards.
Work near a Bunsen flame so rising hot air draws microbes away, and flame the neck of the broth container when opening and closing it.

Ethanol control

Ethanol control it shows that clear zones are due to the plant extract and not the paper or ethanol.

Part 10 of 11Sustainability and plant materials

Sustainability

Sustainability using resources so that the needs of the present are met without depleting them for future generations.

Renewable resources, such as solar energy, do not run out in our lifetime.
Fossil fuels are non-renewable because they take millions of years to form.
Replanting trees after logging is sustainable, whereas making oil-based plastics is limited by a finite supply.

Plant fibres

Plant fibres they use less fossil fuel and the plants can be replanted.
Fibres are biodegradable, unlike most oil-based plastics, so products are broken down by microbes and cause less pollution.
Growing and processing plants is cheaper than extracting oil, which helps developing countries.
Plant fibre ropes are typically not as strong as plastic ones.

Starch

Starch it can be made into bioplastics and bioethanol fuel, which is more sustainable than oil-based alternatives because crop plants are renewable.

Part 11 of 11More from the specification

Plant stems

Plant stems tissue types include xylem for water, phloem for assimilates and sclerenchyma fibres for support

Identifying tissue

Identifying tissue stains such as phloroglucinol show lignified xylem in stem sections viewed under the microscope

Properties of fibres

Properties of fibres long cellulose fibres with strong walls are used for rope and textiles

Antimicrobial properties

Antimicrobial properties plants make compounds that kill bacteria, and tests use inhibition zones on agar, ensuring aseptic technique and controls

Property

A feature that something has, such as reflection for waves.

Key terms

Term	Meaning
Middle lamella	The outer layer of the plant cell that glues adjacent cells together.
Plasmodesmata	Cytoplasmic threads that connect neighbouring plant cells.
Translocation	Transport of organic compounds in phloem from sources to sinks.
Tensile strength	The maximum load a fibre can carry before breaking.
Placebo	A treatment identical in appearance to a drug with no active ingredient.
Double blind trial	A trial in which neither patient nor doctor knows who receives the drug.
Sustainability	Using resources without depleting them for future generations.
Aseptic technique	Methods that prevent contamination of cultures by unwanted microbes.

Avoid these mistakes

Saying xylem has living cells with organelles — mature xylem is dead and lignified.

Saying phloem carries water and minerals — phloem carries sucrose and other assimilates.

Omitting a control disc soaked in ethanol — without it, clear zones cannot be attributed to the plant extract.

Describing cellulose as made from alpha-glucose — cellulose is beta-glucose, with alternate molecules rotated 180°.

Last updated: 15 October 2026