IB Bio Chap 9 Questions
Outline the role of phloem in active translocation of sugars (sucrose) and amino acids from source (photosynthetic tissue and storage organs) to sink (fruit, seeds, roots).
'Phloem tissue' transports sugars and amino acids from sources (photosynthetic tissue-leaves and stems- and storage organs) to sinks which include the fruits, seeds and roots of the plant. This 'transportation method' is known as Active Translocation and requires energy (ATP Organic molecules (sugars, amino acids) move from their source (photosynthetic tissue or storage organs) into a tube system called the phloem Sugars are transported as sucrose (because it is soluble but metabolically inert) in the fluid of the phloem (called the sap) They are actively loaded into the phloem by companion cells, creating a high concentration which draws water from the xylem via osmosis The sap volume and pressure consequently increase to create mass flow which drives the sap along the phloem The organic molecules are actively unloaded by companion cells and stored in the sink (fruits, seeds, roots) Sucrose is stored as starch (insoluble), while the water in the phloem is released (now that solute concentration is low) and returned to the xylem
Outline the role of α-amylase during the germination of seeds
(breakdown) of starch to maltose
A man attaches a bird box to the trunk of a dicotyledonous tree. A few years later he returns to the tree and finds that his bird box is [1 mark] still attached and the tree is much taller. How high will his bird box be from the ground? A. Unchanged as growth from the apical meristem would be above the box. B. Unchanged as growth from the lateral meristem would be above the box. C. Higher as growth from the apical meristem would be below the box. D. Higher as growth from the lateral meristem would be below the box
A
What part of the human body is most similar in function to the spongy mesophyll layer in a leaf? A. Alveoli in the lungs B. Erythrocytes in the blood C. Villi in the small intestine D. Sweat glands in the skin
A
What steps occur in germination after water uptake? [1 mark] A. Gibberellin is produced, followed by amylase activation B. Gibberellin stimulates photosynthesis to begin in the cotyledons C. Amylase breaks down starch to glucose which activates the embryo D. Amylase synthesis followed by activation of gibberelli
A
Which abiotic factors affect transpiration in plants? [1 mark] A. temperature, humidity and wind B. pH, temperature and salinity C. light, pH and humidity D. humidity, temperature and salinity
A
State that dicotyledonous plants have apical and lateral meristems
A meristem is a tissue in a plant consisting of undifferentiated cells (meristematic tissue) and are found in zones where growth can take place Meristematic cells are analogous to stem cells in animals, however have specific regions of growth and development (unlike stem cells) Dicotyledonous plants have apical and lateral meristems
Identify modifications of roots, stems and leaves for different functions: bulbs, stem tubers, storage roots and tendrils
A storage organ is a part of a plant specifically modified to store energy (e.g. carbohydrates) or water They are usually found underground (better protection from herbivores) and may result from modifications to roots, stems or leaves: Storage roots: Modified roots that store water or food (e.g. carrots) Stem tubers: Horizontal underground stems that store carbohydrates (e.g. potato) Bulbs: Modified leaf bases (may be found as underground vertical shoots) that contain layers called scales (e.g. onion) Some plants (called succulents) have modified leaves or stems (thickened, fleshy and wax-covered) to enable water storage (e.g. cacti) Other plants (e.g. vines) have modifications to their leaf or stem to enable climbing support and attachment - these are called tendrils
Outline the metabolic processes that occur in starchy seeds during germination.
After rehydration of the seed, Gibberellic Acid (GA)) gets released. The trigger of GA starts the production of amylase. Amylase breaks starch into maltose, (it breaks the starch in food reserve) then the amylase breaks it into glucose. Glucose is what we want because it can be used in cell respiration and make cellulose for cell walls. There are other enzymes also used to break proteins into amino acids.
Explain how aphid stylets can be used to study the movement of solutes in plant tissues.
Aphids are a group of insects, belonging to the order Hemiptera, which feed primarily on sap extracted from phloem Aphids are positioned along the plant's length and encouraged to feed on the phloem sap Once feeding has commenced, the aphid stylet is severed and sap continues to flow from the plant at the selected positions The sap is then analysed for the presence of radioactively-labelled sugars The rate of phloem transport (translocation rate) can be calculated based on the time taken for the radioisotope to be detected at different positions along the plant's length
Auxin is a protein. Explain its role in phototropism.
Auxin is a plant hormone; produced by the tip of the stem/shoot tip; has 3 main roles: Causes transport of H+ ions from cytoplasm to cell wall; which decreases pH of cell wall, causing bonds between cell wall fibres to break; making cell walls flexible; Auxin makes cells enlarge/grow; during positive phototropism (growth towards light); When shoot tip senses direction of (brightest) light; causing auxin to move to side of stem with least light/darker side, which causes cells on dark side to elongate; Auxin also alters gene expression to promote cell growth;
How do mineral ions in the soil move to the root through the soil? A. Osmosis B. Mass flow of water C. Translocation D. Through phloem
B
How does phytochrome control flowering in plants? A. Pfr turns into Pr in the light, causing short-day plants to flower. B. Pr turns into Pfr in the light, causing long-day plants to flower. C. Pfr turns into Pr in the dark, causing long-day plants to flower. D. Pr turns into Pfr in the dark, causing short-day plants to flower
B
Plants develop brightly coloured flowers to attract animals. Which process is directly assisted by this adaptation? A. Seed dispersal B. Pollination C. Fertilization D. Germination
B
Which of the following are characteristics of monocotyledonous plants? I. Parallel venation of leaves II. Floral organs in multiples of four III. Fibrous adventitious roots A. I and II only B. I and III only C. II and III only D. I, II and III
B
What are the main structures in a bulb and their function? A. Flowers for sexual reproduction B. Enlarged roots for nutrient absorption from the soil C. Swollen leaf bases for food storage D. Thickened stems for water storage
C
What causes stomata to close? A. Increase in the turgor of the guard cells B. A high level of CO2 in the leaf tissues C. The presence of abscisic acid D. Movement of K+ into the guard cells
C
What controls the flowering process in long-day plants? A. Pfr is converted by red light to Pr which acts as a promoter of flowering. B. Pr is converted by red light to Pfr which acts as an inhibitor of flowering. C. Pr is converted by red light to Pfr which acts as a promoter of flowering. D. Pfr is converted by red light to Pr which acts as an inhibitor of flowering
C
Which process happens first during germination of a starchy seed? [1 mark] A. Formation of gibberellin B. Production of amylase C. Absorption of water D. Conversion of starch into monosaccharides
C
What is a role of xylem? [1 mark] A. It absorbs minerals from the soil by active transport. B. It translocates amino acids from source to sink. C. It carries glucose to the leaves. D. It contributes to the plant support with lignified walls.
D
Explain how minerals move into plants
Fertile soil typically contains negatively charged clay particles to which positively charged mineral ions (cations) may attach Minerals that need to be taken up from the soil include Mg2+ (for chlorophyll), nitrates (for amino acids), Na+, K+ and PO43- Mineral ions may passively diffuse into the roots, but will more commonly be actively uploaded by indirect active transport Root cells contain proton pumps that actively expel H+ ions (stored in the vacuole of root cells) into the surrounding soil The H+ ions displace the positively charged mineral ions from the clay, allowing them to diffuse into the root along a gradient Negatively charged mineral ions (anions) may bind to the H+ ions and be reabsorbed along with the proton
Explain how flowering is controlled in long-day and short-day plants.
Flowering in long-day and short-day plants is controlled by a pigment called phytochrome. This pigment exists in two forms, Pr and Pfr, which can be converted into each other. The Prform is the inacctive form and absorbs red light with a wavelength of 660 nm. When Prabsorbs red light it is rappidly converted to the active Pfr form. The Pfr form absorbs far red light with a wavelength of 730 nm and then rapidly converts to the Pr form again in day light. However, normal day light contains more light of wavelength of 660 nm rather than 730 nm. This means that in normal day light, there is more Pfr than there is Pr. However the Pr form is the more stable of the two and therefore during the dark hours Pfr is slowly converted back into Pr. The amount of Pfr remaining after the dark nights is most likely the way plants can time the legth of dark periods. If the dark period is short, this means there will be a lot of Pfr as not much of it will have converted back into Pr. If the dark period is long, less Pfr will be available as most of it will have been converted back into Pr. Furthermore, Pfr promotes flowering in long day plants and inhibits flowering in short-day plants. Therfore, during long dark periods (autumn-winter) short day plants will flower as most of the Pfr has been converted back into Pr in the morning. On the other hand, long-day plants flower in the shorter dark periods (spring-summer) as enough Pfr remains in the morning to promote flowering.
Explain the conditions that are needed to allow a seed to germinate
Germination is the emerging and growth of an embryonic plant from a seed. It requires certain conditions, such as water, heat and oxygen. If conditions are not favourable then the seed may remain dormant. This way the seed can survive adverse conditions and only start to germinate when conditions become more favourable. Water is needed to rehydrate the cells of the seed. This is vital for the activation of certain enzymes which start the metabolism of the seed. Without water the embryo root and shoot are not able to grow. Also water causes the seed to swell and this leads to the bursting of the seed coat which enables the plant to emerge from the seed. In addition, heat is needed for germination as the enzyme activity inside the seed depends on it. However, appropriate temperatures are needed. If it is too hot or too cold the enzyme activity will be too low for germination. Therefore, seeds usually remain dormant if heat conditions are not favourable. Finally, oxygen is needed for metabolism. It is used in aerobic cell respiration to provide the energy for the growth of the plant until the first leaves emerge. Once the leaves emerge, photosynthesis can then provide the energy needed for growth.
Outline the conditions needed for the germination of a typical seed
Germination is the emerging and growth of an embryonic plant from a seed. It requires certain conditions, such as water, heat and oxygen. If conditions are not favourable then the seed may remain dormant. This way the seed can survive adverse conditions and only start to germinate when conditions become more favourable. Water is needed to rehydrate the cells of the seed. This is vital for the activation of certain enzymes which start the metabolism of the seed. Without water the embryo root and shoot are not able to grow. Also water causes the seed to swell and this leads to the bursting of the seed coat which enables the plant to emerge from the seed. In addition, heat is needed for germination as the enzyme activity inside the seed depends on it. However, appropriate temperatures are needed. If it is too hot or too cold the enzyme activity will be too low for germination. Therefore, seeds usually remain dormant if heat conditions are not favourable. Finally, oxygen is needed for metabolism. It is used in aerobic cell respiration to provide the energy for the growth of the plant until the first leaves emerge. Once the leaves emerge, photosynthesis can then provide the energy needed for growth.
Explain how triose phosphate is produced and used in the chloroplasts of a plant.
Glycerate 3-phosphate is reduced during the reduction reactions to a three-carbon sugar called triose phosphate. Energy and hydrogen is needed for the reduction and these are supplied by ATP and NADPH + H+ (both produced during light-dependent reactions) respectively. Two triose phosphate molecules can then react together to form glucose phosphate. The condensation of many molecules of glucose phosphate forms starch which is the form of carbohydrate stored in plants. However, out of six triose phosphates produced during the reduction reactions, only one will be used to synthesise glucose phosphate. The five remaining triose phosphates will be used to regenerate RuBP. The regeneration of RuBP is essential for carbon fixation to continue. Five triose phosphate molecules will undergo a series of reactions requiring energy from ATP, to form three molecules of RuBP. RuBP is therefore consumed and produced during the light-independent reactions and therefore these reactions form a cycle which is named the Calvin cycle.
Vascular plants can be found in a wide variety of ecosystems. Outline active transport in phloem tissue.
Hydrogen ions (H+) are actively transported out of phloem cells by proton pumps (involves the hydrolysis of ATP) The concentration of hydrogen ions consequently builds up outside of the cell, creating a proton gradient Hydrogen ions passively diffuse back into the phloem cell via a co-transport protein, which requires sucrose movement This results in a build up of sucrose within the phloem sieve tube for subsequent transport from the source
Explain how abiotic factors affect the rate of transpiration in terrestrial plants.
Light - Rate of transpiration is greater when light is available, as stomata tend to close in the dark. Wind - Wind increases transpiration rate by removing the humidity around the leaf produced by transpiration. Humidity - Water diffuses out of the leaf, down its concentration gradient, from a high concentration gradient (inside the leaf) to a low concentration gradient in the air. The lower concentration gradient in the air is vital for transpiration. Humidity is the water vapour in the air, thus a rise in humidity means a larger concentration of water vapour in the air & results in a decrease in the rate of transpiration. Temperature - As temperature rises, so does the rate of transpiration. Heat is vital for the evaporation of water vapour from the cell walls of spongy mesophyll cells. Rising temperature levels lead to an increase in evaporation rates, thereby increasing transpiration rate. Higher temperatures also increase the rate of diffusion between air spaces inside the leaf and the air outside.
Explain the processes by which minerals are absorbed from the soil into the roots.
Minerals move into the root system via the following pathways: Diffusion: Movement of minerals along a concentration gradient Mass Flow: Uptake of mineral ions by means of a hydrostatic pressure gradient Water being taken into roots via osmosis creates a negative hydrostatic pressure in the soil Minerals form hydrogen bonds with water molecules and are dragged to the root, concentrating them for absorption Fungal Hyphae: Absorb minerals from the soil and exchange with sugars from the plant (mutualism)
List the ways in which mineral ions in the soil move into the root
Minerals move into the root system via the following pathways: Diffusion: Movement of minerals along a concentration gradient Mass Flow: Uptake of mineral ions by means of a hydrostatic pressure gradient Water being taken into roots via osmosis creates a negative hydrostatic pressure in the soil Minerals form hydrogen bonds with water molecules and are dragged to the root, concentrating them for absorption Fungal Hyphae: Absorb minerals from the soil and exchange with sugars from the plant (mutualism)
Outline the role of the phloem in active translocation of sugars (sucrose) and amino acids from source (photosynthetic tissue and storage organs) to sink (fruits, seeds, roots)
Organic molecules (sugars, amino acids) move from their source (photosynthetic tissue or storage organs) into a tube system called the phloem Sugars are transported as sucrose (because it is soluble but metabolically inert) in the fluid of the phloem (called the sap) They are actively loaded into the phloem by companion cells, creating a high concentration which draws water from the xylem via osmosis The sap volume and pressure consequently increase to create mass flow which drives the sap along the phloem The organic molecules are actively unloaded by companion cells and stored in the sink (fruits, seeds, roots) Sucrose is stored as starch (insoluble), while the water in the phloem is released (now that solute concentration is low) and returned to the xylem
Explain the role of auxin in phototropism
Phototropism is the growing or turning of an organism in response to a unidirectional light source Auxins (e.g. IAA) are plant hormones that are produced by the tip of a shoot and mediate phototropism Auxin makes cells enlarge or grow and, in the shoot, are eradicated by light The accumulation of auxin on the shaded side of a plant causes this side only to lengthen, resulting in the shoot bending towards the light Auxin causes cell elongation by activating proton pumps that expel H+ ions from the cytoplasm to the cell wall The resultant decrease in pH within the cell wall causes cellulose fibres to loosen (by breaking the bonds that hold them together) This makes the cell wall flexible and capable of stretching when water influx promotes cell turgor Auxin can also alter gene expression to promote cell growth (via the upregulation of expansins)
Outline the adaptations of plant roots for absorption of mineral ions from the soil
Plants take up water and essential minerals via their roots and thus need a maximal surface area in order to optimise this uptake The monocotyledon root has a fibrous, highly branching structure which increases surface area for maximal absorption The dicotyledon root has a main tap root which can penetrate deeply into the soil to access deeper reservoirs of water and minerals, as well as lateral branches to maximise surface area The root epidermis may have extensions called root hairs which further increase surface area for mineral and water absorption These root hairs have carrier proteins and ion pumps in their plasma membrance, and many mitochondria within the cytoplasm, to aid active transport
Outline pollination, fertilization and seed dispersal
Pollination is the transfer of pollen from an anther to a receptive stigma. Meanwhile fertilization is when the pollen grain germinates to produce a pollen tube that carries down the two male nuclei. Seed dispersal is the scattering of seeds using other animals or mother nature (wind) to scatter the seeds. It's a way for the plant to get the babies away from them, but still allow them to grow.
Describe the transport of water through an angiosperm root system. [6]
Root hairs take up water by osmosis; correct reference to root pressure; water moves by either: symplastic pathway through cytoplasm (of cells); by diffusion; apoplastic pathway through (cortex) cell walls; by capillary action; Casparian strip blocks apoplastic pathway; so water passes into xylem; Transpiration causes the pull of water (through plant);
Compare growth due to apical and lateral meristems in dicotyledonous plants
Similarities: Both are composed of totipotent cells (able to divide and differentiate) Both are found in dicotyledonous plant
Explain how water is carried by the transpiration stream, including the structure of xylem vessels, transpiration pull, cohesion, adhesion and evaporation
Some of the light energy absorbed by leaves changes into heat, converting water in the spongy mesophyll into vapour This vapour diffuses out of the stomata and is evaporated, creating a negative pressure gradient in the leaf New water is drawn from the xylem (mass flow), which is replaced by water from the roots (enters from soil via osmosis) The flow of water through the xylem from the roots to the leaf is called the transpiration stream Water rises through xylem vessels because of two qualities: Cohesion: Water molecules are weakly attracted to each other via hydrogen bonds Adhesion: Water molecules form hydrogen bonds with the xylem cell wall These properties create a suction effect (or transpiration pull) in the xylem The xylem has a specialised structure to facilitate transpiration: The inner lining is composed of dead cells that have fused to create a continuous tube These cells lack a cell membrane, allowing water to enter the xylem freely The outer layer is perforated (contains pores), allowing water to move out of the xylem into the leaves The outer cell wall contains annular lignin rings which strengthens the xylem against the tension created by the transpiration stream
Explain the process of mineral ion absorption from the soil into roots by Active Transport.
The concentration of mineral ions inside the plant's roots is a lot higher than that found in the soil. Thus, mineral ions have to be transported into the roots by active transport. Protein pumps exist in the plasma membranes of root cells. Many types exist for the absorption of many different mineral ions. Active transport requires ATP production by mitochondria (aerobic cell respiration- oxygen is needed) and so, the root cells also contain lots of mitochondria. The branching of the roots and the formation of 'root hairs' increases surface area for the absorption of mineral ions- by active transport.
State that guard cells can regulate transpiration by opening and closing stomata
The transpiration pull is generated by the negative hydrostatic pressure created by the evaporation of water vapor from the leaf Guard cells line stomata and regulate transpiration by controlling how much water vapor can exit the leaf When stomata are open the rate of transpiration will be higher than when they are closed
Define the term transpiration and explain the factors that can affect transpiration in a typical terrestrial plant
Transpiration is the loss of water vapour from the leaves and stems of plants. Light Increasing the intensity of light increases the rate of transpiration Light stimulates the opening of stomata (gas exchange required for photosynthesis to occur) Some of the light energy absorbed by leaves is converted into heat, which increases the rate of water evaporation Temperature Increasing the temperature increases the rate of transpiration Higher temperatures cause an increase in water vaporisation in the spongy mesophyll and an increase in evaporation from the surface of the leaf This leads to an increase in the diffusion of water vapour out of the leaf (via the stomata) which increases the rate of transpiration Wind Greater air flow around the surface of the leaf increases the rate of transpiration Wind removes water vapour (lower concentration of vapour on leaf surface), increasing the rate of diffusion from within the spongy mesophyll Humidity Increasing the humidity decreases the rate of transpiration Humidity is water vapour in the air, thus a high humidity means there is a high concentration of water vapour in the air This reduces the rate of diffusion of water vapour from inside the leaf (concentration gradient is smaller resulting in less net flow)
Vascular plants can be found in a wide variety of ecosystems. Explain how a plant replaces the water it loses in transpiration.
Transpiration is the loss of water vapour from the stems and leaves of plants Light energy converts water in the leaves to vapour, which evaporates from the leaf via stomata New water is absorbed from the soil by the roots, creating a difference in pressure between the leaves (low) and roots (high) Water will flow, via the xylem, along the pressure gradient to replace the water lost from leaves (transpiration stream)
Describe how water is carried by the transpiration stream
Transpiration: Water loss (from plant) by evaporation; Transpiration Stream: Flow of water, through xylem, from roots to leaves; Evaporation from spongy mesophyll cells; replaced by osmosis from the xylem; Water vapour also lost by diffusion through stomata; also replaced by osmosis from xylem; Water pulled out of xylem creates suction/low pressure/tension; which causes transpiration pull; creating transpiration stream; Water molecules are cohesive; and adhesive; due to hydrogen bonding/polarity of water molecules; Xylem vessels are thin (hollow) tubes; to which water sticks to (adhesion); creating the
Explain how auxin controls the response of a plant to light
Tropisms are directional movement responses which occur due to external environmental stimuli. The direction of the stimulus affects the direction of movement. Tropisms can either be negative or positive. Positive tropisms are the directional movement towards the stimulus while negative tropisms are the directional movement away from the stimulus. Examples of stimuli causing tropisms in plants are gravity and light Roots will grow towards gravity while the plant shoot will grow upwards in the opposite direction. The directional movement of plants in response to light is called phototropism. As seen with gravity, the plant's roots will grow away from the light, into the soil (negative phototropism) while the plant shoot will grow towards the light (positive phototropism). Positive phototropism seen at the tips of plant shoots is made possible due to plant hormones called auxins. Auxins are produced at the tips of plant shoots and then translocate to the darker side of the shoot tip and stem which is receiving less light. This translocation is made possible via auxin efflux carriers which are unevenly distributed in the plant tissue. Once auxins reach the shaded side of the plant, they cause the elongation of cells so that the shaded side grows faster than the brighter side, thereby promoting the bending of the plant shoot towards the light. Auxins do so by binding to auxin receptors on cells. The binding of auxin causes the transcription of certain genes within those cells and therefore the production of specific proteins which affect growth. Auxins allow the expelling of protons (hydrogen ions) into the cell walls of the cells on the shaded side, decreasing the pH inside the cells and in doing so activate specific enzymes which break down cellulose microfibrils within the cell wall. This loosens the cell wall and allows cell elongation. So to conclude, auxins are very important in the control of plant growth towards the light and thereby allow the plant to increase its rate of photosynthesis.
Explain the relationship between the distribution of tissues in the leaf and the function of these tissues
Upper Epidermis Function: Main function is water conservation (secretes cuticle to create a waxy outer boundary) Distribution: On top of leaves where light intensity and heat are greatest Palisade Mesophyll Function: Main photosynthetic tissue (cells contains many chloroplasts) Distribution: Upper half of leaf where light intensity is greatest (upper epidermal cells are transparent) Spongy Mesophyll Function: Main site of gas exchange (made of loosely packed cells with spaces) Distribution: Lower half of leaf, near the stomatal pores (where gases and water are exchanged with the atmosphere) Vascular Tissue Function: Transport of water (xylem) and the products of photosynthesis (phloem) Distribution: Found in middle of leaf (allowing all cells optimal access)
Describe how water is carried through a flowering plant
Water will follow the mineral ions into the root via osmosis - moving towards the region with a higher solute concentration The rate of water uptake will be regulated by specialised water channels (aquaporins) on the root cell membrane Once inside the root, water will move towards the xylem either via the cytoplasm (symplastic) or via the cell wall (apoplastic) In the symplastic pathway, water moves continuously through the cytoplasm of cells (connected via plasmodesmata) In the apoplastic pathway, water cannot cross the Casparian strip and is transferred to the cytoplasm of the endodermis
State that the plant hormone abscisic acid causes the closing of the stomata
When a plant begins to wilt from water stress, dehydrated mesophyll cells release the plant hormone abscisic acid (ABA) Abscisic acid triggers the efflux of potassium from guard cells, decreasing the water pressure within these cells and making them flaccid This causes the stomatal pore to close
Angiospermophyta have vascular tissue (xylem and phloem) that bryophyta lack. Suggest advantages that vascular tissue confers.
Would make it easier to stand upright against gravity/structural support; reduced/few leaves/needles to lower surface area; could put leaves higher in the air to get more sunlight; transport of water supply/nutrients from roots to other tissues; could (more efficiently) transport/translocate sugars/food from leaves for storage;
Which of the following are features of the dicotyledonous plants? I. Parallel leaf veins II. Flower parts in groups of three III. Two seed-leaves (cotyledons) A. III only B. II and III only C. I and II only D. I, II and III
a
. Describe the importance of water to living organisms.
a. coolant in sweat/in transpiration; b. water has a high heat of vaporisation / heat taken when hydrogen bonds break; c. water is cohesive so can pulled up/so can be moved under tension in xylem; d. water is an excellent/universal solvent/dissolves many different substances; e. medium for transport in blood/xylem/phloem; f. medium for metabolic reactions / (metabolic) reactions happen dissolved in water; g. surface tension due to cohesion allows organisms to live on water surface; h. water has high heat capacity so much energy required to change its temperature; i. ice floats so lakes/oceans do not freeze allowing life under the ice; j. high heat capacity so stable habitat/so temperature of water changes slowly; k. used in chemical reactions/photosynthesis/hydrolysis in organisms;
Following germination of seeds, plants undergo a rapid increase in the number of cells. Describe stages in the cell cycle that result in this increase of cells.
a. growth phase/G-1: synthesis of proteins/cytoplasm/organelles; b. synthesis phase/S-phase: replication of DNA; c. second growth phase/G-2: continued growth of cytoplasm/molecular synthesis/duplication of organelles; d. prophase: chromosomes super-coil to prepare for mitosis / nuclear envelope disappears / spindle fibres form; e. metaphase: chromosomes line up at equatorial/metaphase plate / spindle fibres attach to centromeres/chromosomes; f. anaphase: chromatids move along microtubules/spindle fibres move chromatids toward opposite poles; g. telophase: nuclear membranes form around each cluster of chromosomes; h. cytokinesis: new plasma membrane forms between the nuclei / cell plate forms; i. a new cell wall forms; j. (mitosis) results in two cells with identical nuclei;
State two types of meristem found in plants.
apical and lateral
What is the effect of abscisic acid on transpiration? A. It increases transpiration by causing the stomata to open. B. It decreases transpiration by causing the stomata to close. C. It increases transpiration by decreasing the humidity inside the leaf. D. It decreases transpiration by increasing the humidity inside the leaf
b
Which plant hormone is responsible for the closing of the stomata? A. Gibberellic acid B. Abscisic acid C. Phytochromes D. Ethylene
b
What generates new cells in dicotyledonous plants? I. Apical meristems II. Lateral meristems III. Phloem A. I only B. II only C. I and II only D. I, II and III
c
What is transported in xylem tissue? [1 mark] A. Sucrose from leaves to fruits B. Starch from leaves to storage organs C. Water from roots to leaves D. Salts from soil to roots
c
State two methods by which terrestrial plants support themselves
cellulose cell wall / turgor / lignin / lignified xylem
1. How do auxins cause plant shoots to grow towards light? [1 mark] A. Increase cell division on the side of the stem near the light source B. Increase cell division on the side of the stem away from the light source C. Increase cell elongation on the side of the stem near the light source D. Increase cell elongation on the side of the stem away from the light source
d
Describe how plants carry out gas exchange in the leaves.
gases/O and CO enter/exit the leaf through the stomata; by diffusion / down the concentration gradient; photosynthesis maintains concentration gradients/high O and low CO in the leaf; guard cells open the stomata during the day / close the stomata at night; gases/O /CO move through air spaces in the spongy (mesophyll); CO dissolves in moisture in (mesophyll) cell walls;
Outline how and where energy is stored in plants.
glucose (from photosynthesis) stored as starch; b. starch stored (as granules) in chloroplast/in plastids; c. (starch stored) in seeds/storage roots/stem tubers; d. stored as lipids/oils; e. (lipid/oils storage) in seeds; f. lipids store twice as much energy per gram as starch;
Outline the process of water uptake by root epidermis cells. [5] Describe the process of water uptake and movement in roots.
lants actively transport minerals from soils; creating a solute gradient within root; which draws water through root epidermis cell by osmosis; a passive process; root hairs on epidermis cell increase surface area for osmosis; and allow absorption of water from soil further away from the root; water absorbed by the cell wall of the root hair cell is called the apoplastic route; water moves by capillary action through this route; some water travels via symplastic pathway; apoplast water can't bypass Caspian strip of endodermis; so it enters xylem within vascular cylinder/stele
Outline the adaptations of plant roots for absorption of mineral ions from the soil.
mineral ions are absorbed by active transport; large surface area; branching (increases surface area); root hairs; root hair cells have carrier protein/ion pumps (in their plasma membrane); (many) mitochondria in root (hair) cells; to provide ATP for active transport; connections with fungi in the soil/fungal hyphae;
Photosynthesis and transpiration occur in leaves. Explain how temperature affects these processes.
photosynthesis rate increases as temperature rises (up to an optimum temperature); (due to) increase in the rate of enzyme catalysed reactions/light independent reactions/the Calvin cycle; (steep) drop in rate of photosynthesis above the optimum; at high temperatures enzymes/Rubisco/RuBP carboxylase denature(s); graph with correctly labelled axes showing relationship between temperature and rate of photosynthesis; transpiration rate increases as temperature rises; (energy/heat leads to more) evaporation of water (in the leaf); faster diffusion of water vapour at higher temperatures; relative humidity falls as temperature rises / warmer air can hold more water vapour; stomata may close at very high temperatures reducing the transpiration rate; some plants open their stomata at very high temperatures to cool by transpiration;
State the role of four named minerals needed by living organisms
sulfur - part of amino acids / proteins; calcium - strengthening/formation of bones / muscle contraction / synaptic transmission; phosphorus - formation of nucleic acids / ATP / GTP / NADP / phospholipids; iron - formation of hemoglobin / transport of oxygen; sodium - nerve impulse / sodium-potassium pump / osmoregulation; potassium - nerve transmission / sodium-potassium pump / osmoregulation; magnesium - part of chlorophyll molecule;
Outline adaptations of xerophytes
xerophytes are plants that live in dry conditions; reduced leaves/spines to prevent water loss (by transpiration); rolled leaves to prevent water loss / stomata on the inside / sunken stomata; thick waxy cuticle/hairs on leaves to prevent water loss (by transpiration); reduced stomata to prevent water loss (by transpiration) / stomata on one side of leaf; deep/widespread roots to obtain more water; special tissue for storing water; take in carbon dioxide at night / CAM plant to prevent water loss;