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Biology 🦠 > Chapter 12: Flowering plants > Flashcards

Chapter 12: Flowering plants Flashcards

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1
Q

External structure of leaf

A
  1. Network of veins
  2. Leaf blade
  3. Leaf arrangements
  4. Leaf Stalk
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2
Q

Network of veins

A
  • veins carry water and mineral salts to the cells in the leaf blade
  • veins also carry manufactured food from these cells to other parts of the plant
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3
Q

Leaf blade

A
  • it has a flat surface compared to it volume
  • enables it to obtain the max amount of light for photosynthesis
  • large, thin blade also allow CO2 to rapidly reach the inner cells of the leaf
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4
Q

Leaf arrangement

A
  • laves are always organised around stem in a regular pattern
  • leave often grow in pairs or singly in an alternate arrangement
  • ensures that the leaves are not blocking one another from light and that each leaf receive sufficient amount of light
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5
Q

Leaf stalk

A
  • holds the leaf blade away from stem to allow leaf to obtain sufficient light and air
  • some plants don’t have leaf stalk, they have long leaf blades instead
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6
Q

Internal structure of leaf

A
  1. Upper epidermis
  2. Palisade mesophyll
  3. Spongy mesophyll
  4. Lower epidermis
  5. Cuticle
  6. Stoma (Plural: Stomata)
  7. Guard Cell
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7
Q

Upper epidermis

A
  • a single layer of closely packed cells
  • covered on the outside by waxy and transparent cuticle
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8
Q

Mesophyll

A
  • lies between upper and lower epidermis
  • main site for photosynthesis
  • contains palisade and spongy mesophyll
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9
Q

Palisade mesophyll

A
  • consists of 1/2 layers of closely packed, long cylindrical cells
  • contains numerous chloroplasts
  • specialised for photosynthesis
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10
Q

Spongy mesophyll

A
  • contains cells with irregular shape
  • has numerous large intercellular spaces among the loosely packed cells
  • carries out photosynthesis, but contains fewer chloroplast than the palisade mesophyll
  • cells covered with thin film of moisture
  • contains transport tissue (xylem and phloem which are grouped tgt to form a vascular bundle)
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11
Q

Lower Epidermis

A
  • beneath mesophyll layer
  • consists of a single layer of closely packed cells
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12
Q

Cuticle

A
  • cells are covered by an outer layer of cuticle
  • reduced water loss through epidermal cells
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13
Q

Stoma (plural: Stomata)

A
  • minute openings in lower epidermal
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14
Q

Guard cells

A
  • found in lower epidermis
  • a pair surrounds each stoma and helps regulate rate of transpiration by opening and closing stoma
  • contains chlorophyll which are not present in other epidermal cells
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15
Q

How the leaf is adapted for photosynthesis

A
  1. Waxy cuticle on lower and upper epidermis
  2. Stomata present in the epidermal layers
  3. Chloroplasts containing chlorophyll in all mesophyll cells
  4. More chloroplasts in upper palisade tissue
  5. Interconnecting system of air spaces in spongy mesophyll
  6. Veins containing xylene and phloem situated close to mesophyll cells
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16
Q

Waxy cuticle on upper and lower epidermis

A
  • reduced water loss through evaporation from leaf
  • transparent fro light to enter leaf
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17
Q

Stomata present in epidermal layers

A
  • stomata open in presence of light, allowing CO2 to diffuse in and oxygen diffuse out of the leaf
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18
Q

Chloroplasts containing chlorophyll in all mesophyll cells

A
  • chlorophyll absorbs energy from light and transfers it to the chemical stores of energy in glucose molecules
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19
Q

More chloroplasts in upper palisade

A
  • more light can be absorbed near leaf surface
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20
Q

Interconnecting system of air spaces in spongy mesophyll

A
  • allows rapid diffusion of C02 and O2 into and out of mesophyll cells
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21
Q

Veins containing xylem and phloem situated close to mesophyll cells

A
  • xylem transports water and mineral salts to mesophyll cells
  • phloem transports sucrose away from leaf
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22
Q

How guard cells control size of stomata

A
  • stomata generally open in light and close in dark
  • helps to regulate passage of gases between leaf and environment
  • stomata reduces water loss even when plant is in sunlight, such as extremely hot days
  • excess water loss causes guard cells to be flaccid, causing stomata to close
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23
Q

How stomata opens in sunlight

A
  • guard cells manufacture glucose by photosynthesis
  • increase in glucose concentration lowers water potential of cell sap in cell
  • water enters guard cells by osomosis
  • become more turgid and curved cause cell wall around stoma is thicker than other parts of cell
  • hence the cell curves around stoma and stoma opens
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24
Q

How stomata closes on hot sunny day

A
  • leaf loses too much water in strong sunlight, stoma closes
  • excess evaporation of water causes guard cells to become flaccid, thus stomata closes
  • prevents excessive water loss by leaf
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25
Q

How CO2 enter the leaf

A
  1. In daylight, when photosynthesis occurs, CO2 in leaf is rapidly used up. CO2 concentration in leaf becomes lower than that of atmospheric air, so diffusion gradient exist 👉CO2 diffuses from surrounding air through stomata into intercellular air spaces
  2. surfaces of mesophyll cells are always covered by a thin film of water, 👉 C02 will dissolve in it
  3. Dissolved CO2 will then diffuse into cells
26
Q

How water enter the leaf

A
  1. Water molecules move from soil to roots due to higher water potential in soil than in root cells by osmosis
  2. Water molecules move up stem by transpiration pull along xylem vessels
  3. Water molecules from xylem enters by osmosis to mesophyll cells due to water potential diff between xylem and mesophyll cells
27
Q

Function of Xylem

A
  • transport water and dissolved mineral salts from the the roots to the stem and leaves
  • provide mechanical support for plant
28
Q

How a xylem is adapted for its function

A
  • consists of mainly xylem vessels which is a long hollow tube stretching from the root to the leaves
  • a structure made up of many dead cells without cytoplasm or cross-walls
  • reduces resistance to water lowing through the xylem
  • no cross-walls results in continuously narrow long lumen that facilitates the transport of water and mineral salts
  • absence of protoplasm results in hollow vessels that allows efficient transport of water and mineral salts
  • lignin deposition on wall of xylem prevents wall collapse
  • xylem vessels are bundles tgt for added mechanical support
29
Q

Function of phloem

A
  • conduct manufactured food substances from green parts of plant to other parts of plant
30
Q

How the Phloem is adapted to its function

A
  • consists of sieve tubes and companion cells
  • each sieve tube consists of a column of elongated, thin-walled living cells called sieve tube cells
  • sieve plates separating cells have a lot of minute pores
  • a mature sieve tube cell only has a thin layer of cytoplasm inside the cell that is connected to cells above and below through the holes in the sieve plate to allow rapid flow of manufactured food substances through the sieve tubes
  • each sieve tube cell has a companion cell with many mitochondria to provide energy needed for the companion cells to load sugar from mesophyll cells into sieve tube via active transport.
  • companion cell also helps sieve tube cell transport food down the phloem and provide nutrients to it
31
Q

Vascular tissues in stem

A
  • xylem inside, phloem outside and the cambium lies between them
  • Stem is covered by layer of cells called epidermis. The epidermal cells are protected by a waxy, waterproof cuticle that greatly reduces evaporation of water from stem
32
Q

Vascular tissue in leaves

A
  • xylem on top and phloem at the bottom
33
Q

Vascular tissues in roots

A
  • epidermis bears root hair
  • each root hair is long and narrow extension growing out of an epidermal cell
  • long and narrow extension of root hair increases the surface area-to-volume ratio of the root hair cell, which increases rate of absorption
34
Q

Word equation for phtosynthesis

A

Carbon dioxide + water ➡️ glucose + oxygen

35
Q

Chemical equation for photosynthesis

A

6CO2 + 6H2O ➡️ C6H12O6 + 6O2

36
Q

Conditions essential for photosynthesis

A
  1. light
  2. carbon dioxide
  3. chlorophyll
  4. suitable temp
  5. sufficient water
37
Q

Factors that affects rate of photosynthesis

A
  1. Light intensity
  2. Concentration of CO2
  3. Temperature
38
Q

How light intensity affect rate of photosynthesis

A
  • w/o enough light, plant cannot photosynthesise very fast even if there is sufficient water and CO2
  • increasing light intensity increases rate of photosynthesis until a constant rate is reached
  • when more light is supplied to the plant, amount of energy for photosynthesis increase, hence rate of photosynthesis increases
39
Q

How CO2 concentration affects rate of photosynthesis

A
  • plant cannot photosynthesise if there is insufficient amount of light
  • when CO2 concentration increases, rate of photosynthesis increases until a constant rate is reached
  • when there is more CO2, more glucose is produced
40
Q

How temperature affects rate of photosynthesis

A
  • when temp increases to optimal temp, rate of photosynthesis increases
  • when temp increases beyond optimum, rate of photosynthesis decreases because of enzyme denaturation
41
Q

What happens to glucose formed during photosynthesis

A
  1. Glucose is used immediately for cellular respiration
  2. When glucose is formed faster than it is removed, excess glucose is converted to starch before being converted back to glucose by enzymes in darkness
  3. Glucose is converted to sucrose
  4. Glucose is converted to amino acids in leaves
  5. Glucose forms fats
42
Q

Why is glucose converted to sucrose

A
  • to be transported to other parts of the plant or to storage organs
  • converted to other forms of storage compounds at storage organs depending on the plant
  • may be converted back to glucose for respiration
  • component of nectar
43
Q

Why is glucose converted into amino acids

A
  • to form proteins used for synthesis of new protoplasm in leaves
  • excess is transported to other parts of plant for synthesis of new protoplasm or storage as proteins
44
Q

Why glucose forms fats

A
  • for storage
  • for cellular respiration
  • synthesis of new protoplasm
45
Q

Why is photosynthesis important

A
  1. It converts light energy from sun into useful chemical energy in plants for animals & other organisms as food
  2. It removes CO2 from atmosphere and releases O2, ensuring survival of organisms and constant levels of O2 and CO2 in atmosphere
  3. Energy produced is stored in fossil fuels, which is released when it is burned, and we use this energy daily
46
Q

What is translocation

A
  • it is the transport of manufactured food substances such as sugars and amino acids, in plants
47
Q

Entry of water into plant

A
  1. Each root hair is a narrow extension of an epidermal cell. It grows between soil particles, coming into close contact with soil solution surrounding it
  2. Thin film of liquid surrounding each soil particle is a dilute solution of mineral salts
  3. Cell sap in root hair cell has lower water potential than soil solution. Water enters root hair via osmosis through the partially permeable cell membrane
  4. Water dilutes cell sap. WP of root hair cell A is higher than WP of root hair cell B. Hence water passes by osmosis from root hair cell into inner cell
  5. This process continues until water enter xylem vessels and move up plant
48
Q

How root hair cells absorb ions/mineral salts

A
  • By active transport when concentration of ions in salt solution is lower than that in root hair cell sap
  • By diffusion when concentration of ions in salt solution is higher than root hair cell sap
49
Q

How root hair cell is adapted to its function of absorption

A
  • root hair is narrow extension of root hair cell 👉 increases surface area-to-volume ratio 👉 increases rate of absorption of water and mineral salts
  • cell membrane prevents cell sap (contains aa, sugars and salts) from leaking out 👉 cell sap as lower WP than soil solution 👉water enters via osmosis
  • contains many mitochondria for aerobic respiration to take place to release energy for active transport
50
Q

Transpiration

A
  • is the loss of water vapour from aerial parts of plant, mainly through stomata of leaves
51
Q

Transpiration Pull

A
  • Suction force due to transpiration that pulls water up xylem vessels
  • main force for drawing water and mineral salts up the plant
52
Q

How transpiration moves water against gravity

A
  1. Water evaporates from thin film of moisture surrounding mesophyll cells into intercellular air spaces
  2. Water vapour diffuses through stomata to drier air outside leaf
  3. As water evaporates from thin film of moisture, more water moves out from mesophyll cells to replenish it, which decreases WP of cell sap. WP of cell sap become lower then WP of neighbouring cells
  4. Mesophyll cells draw water from cells deeper inside leaf by osmosis
  5. Cells deeper inside leaf then draw water from xylem by osmosis, which creates suction force that pulls the whole column of water up xylem vessels (transpiration pull)
53
Q

Importance of transpiration

A
  • pulls up water and mineral salts from roots to stem & leaves
  • evaporation of water from surface of cells in leaves cools the plant, preventing from getting scorched by sun
  • water transported wan be used for photosynthesis, to keep cell turgid and replace water lost by cells. Turgid cells keep leaves widely spread out to trap light for photosynthesis
54
Q

Factors that affect rate of transpiration

A
  1. Wind/Air movement
  2. Temperature of air
  3. Light
  4. Humidity
55
Q

How wind/air movement affect transpiration

A
  • water vapour that diffuses out of stomata accumulates outside stomata in still air
  • concentration gradient of water vapour is less steep 👉 rate of transpiration is lowered
  • if wind is present, water vapour does not accumulate since it is blown away
  • concentration gradient is steeper 👉 rate of transpiration increases
  • stronger the wind, the higher the rate of transpiration
56
Q

How temp of air affect transpiration

A
  • when temp increase, rate of evaporation of water from cell surfaces increases
  • when temp increases, rate of transpiration increases
57
Q

How light affects transpiration

A
  • light affects size of stomata on leaf
  • when light is present, stomata opens and becomes wider 👉 increases rate of transpiration
58
Q

How humidity affects transpiration

A
  • when surrounding air is less humid, concentration graduent of water vapour is steeper 👉 rate of transpiration increases
  • increasing humidity causes concentration gradient to be less steep 👉 less transpiration
59
Q

Advantages of wilting

A
  • surface area exposed to light reduces
  • reduce exposure of stomata to atmosphere, reducing rate of water loss through stomata
  • excessive water loss causes guard cells to become flaccid and stomata to close, reducing rate of transpiration
60
Q

Disadvantages of wilting

A
  • amount of CO2 entering decreases since stomata closes, causing CO2 to be limiting factor & rate of photosynthesis to decrease
  • reduces exposure to light, reducing rate of photosynthesis

Biology 🦠 (18 decks)

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