Photosynthesis

Question 1

Site of photosynthesis

Answer 1

• eukaryotic plants so chloroplasts are the cellulat organisms cellular organisms within the leaf where photosynthesis takes place

Question 2

Structure of the leaf

Answer 2

• a large surface area that absorbs as much sunlight possible
• an arrangement of leaves on the plant that minimises overlapping and so avoids the shadowing of one leaf by another
• thin so maximum light is absorbed and diffusion distance is short
• transparent cuticle and epidermis so light can pass through to the photosynthetic mesopyll cells beneath
• long narrow upper mesophyll packed with chloroplasts that collect sunlight
• numerous stomata for gaseous exchange so that all mesophyll cells are only a short diffusion pathway from one
• ## stomata open and close in responses to light intensity change

Question 3

Three main stages to photosynthesis

Answer 3

1) capturing of light energy: by chloroplast pigments such as chloropyll
2) the light dependent reaction: some of the light energy is absorbed and conserved in chemical bonds. During this process an electron flow is created by the effect of light on chlorophyll causing water to split into protons, electrons and oxygen. The products are reduced NADP, ATP and oxygen
3) the light- independent reaction in which hydrogen ions are used to produce sugars

Question 4

Structure and role of chloroplasts in photosynthesis

Answer 4

They are surrounded by double membrane. Inside the chloroplast membrane are two regions:

• The grana: stacks of 100 disc like structures called thylakoids where the light dependent stage takes place. Within the thylakoids is the photosynthetic pigment called chloropyhll . Some thlakoids have tubular extensions that join up with thylakoids in adjacent grana which are called intergranal lamellae
• The stroma is a fluid filled matrix where the light-independent stage of photosynthesis. Within the stroma are a number of other structures such as starch grains

Question 5

The light- dependent reaction of photosynthesis involves the capture of light whose energy is used for two purposes

Answer 5

• add inorganic phosphate to ADP thereby making ATP

- split water into H+ and OH- ions. As the splitting is caused by light and is known as photolysis