ONE EIGHTH CONTEST 2025
Ghana National College - 65 points
Tema Secondary School - 33 points
Effiduase SHCS - 28 points
ONE EIGHTH CONTEST 2025
Mankranso SHS - 43 points
St Paul's SHS, Denu - 23 points
Adonten SHS - 14 points
ONE EIGHTH CONTEST 2025
St. Thomas Aquinas SHS - 51 points
Tamale SHS - 37 points
O'Reilly SHS - 25 points
ROUND 1
PREAMBLE
Give the importance of the given activity during the test of starch in the leaf of a herbaceous plant
1. The leaf is boiled in water
ANSWER: Boiling the leaf in water is crucial because it kills the leaf’s cells, stopping all chemical and metabolic processes. This also softens the leaf tissues and makes the cells permeable, allowing iodine solution to enter and react with any starch present.
2. The leaf is boiled in methylated spirit
ANSWER: Boiling the leaf in methylated spirit removes chlorophyll (the green pigment). This decolorizes the leaf, making it pale. Without chlorophyll, any blue-black color change from iodine becomes clearly visible. It also ensures that photosynthesis stops completely.
3. After boiling in methylated spirit, the leaf is placed in warm water
ANSWER: Placing the leaf in warm water softens it again because methylated spirit makes the leaf hard and brittle. Softening helps to flatten the leaf and makes it easier to observe the iodine color change.
PRACTICE QUESTIONS
1. Name the reagent used to test a leaf for starch.
ANSWER: Iodine solution
2. What colour shows that starch is present?
ANSWER: Blue-black
3. Why is the leaf boiled in water first?
ANSWER: It kills the cells, stops reactions and makes the leaf permeable to iodine
4. Why is the leaf then boiled in methylated spirit?
ANSWER: To remove chlorophyll
5. Why is the methylated spirit heated in a water bath and not over a flame?
ANSWER: It is flammable
6. What colour is iodine solution when no starch is present?
ANSWER: Brown (yellow-brown)
7. Why is the plant kept in the dark before the test?
ANSWER: To use up (destarch) the starch already in the leaves
8. What is the purpose of using a variegated leaf?
ANSWER: To show that chlorophyll is needed for photosynthesis
9. Why is the leaf dipped in warm water after the spirit?
ANSWER: To soften it again after it becomes hard and brittle
10. What colour will the white part of a variegated leaf turn with iodine?
ANSWER: Brown, because it has no starch
11. What does the presence of starch in a leaf show?
ANSWER: That photosynthesis has taken place
12. In what form is glucose stored in leaves?
ANSWER: Starch