Topic 4

Question 1

What is a transverse cross section?

Answer 1

Sections cut through in a structure from right angle to its length

Question 2

What is a longitudinal cross section?

Answer 2

Sections cut along the length of a structure

Question 3

Explain how to dissect a plant stem

Answer 3

• Use a scalpel to cut a cross section of the stem
• Cut as thinly as possible for better viewing under light microscope
• Use tweezers to gently place sections in water to stop drying out
• Transfer each section to dish containing toluidine blue O stain
• Leave for a minute
• Rise off the sections in water
• Mount each one onto a slide
• Place prepared slide under microscope

Question 4

What colour should xylem vessels and sclerenchyma fibres look and why?

Answer 4

Blue-green, TBO stains liginin blue-green

Question 5

What colour should phloem cells and rest of plant tissue look?

Answer 5

Pinkish purple

Question 6

Define “tensile strength”

Answer 6

Maximum load a fibre can take before it breaks

Question 7

Describe the tensile strength of a plant fibre experiment

Answer 7

• Attach fibre to clamp stand
• Hang weight from other end
• Keep adding weights one at a time until fibre breaks
• Record mass needed to break fibre: higher mass: higher tensile strength
• Repeat experiment with different samples of same fibre

Question 8

What variables should be kept constant in plant fibre experiment?

Answer 8

• Temperature

- Humidity

Question 9

Describe how to investigate plant mineral deficiencies.

Answer 9

• Make up 3 nutrient broths containing all essential minerals but vary concentration of one of them in each one e.g one high calcium conc, one medium, one low
• Split 9 test tubes into three groups and fill tubes of each group with one of the three broths
• Take 9 seedlings of the same plant
• Measure mass of each seedling using balance and record
• Suspend root in nutrient broth
• Put cotton wool inside tube opening to support seedling
• Cover outside of test tubes in aluminium foil
• Place all tubes near light source e.g windowsill and leave for 2 weeks
• Top up broth to ensure continuous suspension in liquid
• Carefully remove each plant from test tube and blot dry
• Measure and record new masses
• Calculate mean change in mass for each nutrient broth and any visual differences

Question 10

Why do test tubes need to be covered in aluminium foil in investigating plant deficiencies?

Answer 10

So no light can get to nutrient broth and cause organisms e.g algae to grow

Question 11

What type of plant should be used for investigating mineral deficiencies?

Answer 11

Germinated mung beans that are the same age

Question 12

Describe how to test antimicrobial properties of a plant?

Answer 12

• Take extracts from plants to investigate
• Dry and grind each plant and soak in ethanol [antimicrobial substances: soluble in ethanol]
• Filter off liquid with dissolved plant extract
• Transfer bacteria grown in broth with wire inoculation loop to agar plate
• Spread bacteria over top evenly using loop
• Dip equally sized discs of absorbent paper in plant extracts
• Use control disc only soaked in ethanol [ensures no antimicrobial properties in ethanol/absorbent paper]
• Place on agar plate evenly spread out
• Tape lid on
• Invert
• Incubate
• At 25c for 24 to 48 hours
• Where bacteria doesn’t grow are the inhibition zones - measure diameter

Question 13

Why are bacteria incubated at 25 degrees?

Answer 13

• Low enough to stop human harming pathogens growing

- High enough for bacteria to grow well