Plants Flashcards
(22 cards)
Photosynthesis
-> a chemical process where plants synthesize carbohydrates from raw materials using energy from light
[carbon dioxide + water → glucose + oxygen]
Carbon dioxide from air to leaves and water from roots.
Apart from water and carbon dioxide, light and chlorophyll are needed for photosynthesis to take place. Chlorophyll is a green pigment present in the chloroplasts of plant cells.
Chlorophyll absorbs light energy. The light energy is converted to the chemical energy of glucose molecules.
Photosynthesis occurs in chloroplasts.
USES AND STORAGE OF GLUCOSE
- Used in cellular respiration for energy
- Store as starch (long-term energy stored in granules in cytoplasm)
- Form sucrose for transport in the phloem (more stable than glucose)
- Form cellulose to build cell walls.
- Form nectar to attract pollinators for pollination.
MINERAL IONS
-> soluble inorganic ions that are absorbed by root hair cells (most are insoluble but in plant context they are soluble)
- Mg2+ (Magnesium ions) – to make chlorophyll
- NO3- (Nitrate ions) – to make animo acids, building blocks of protein
LIMITING FACTORS OF PHOTOSYNTHESIS
- Light intensity - the rate of photosynthesis increases as the intensity of light increases, but only up to a certain point (due to fixed number of chloroplasts)
- CO2 concentration - the rate of photosynthesis increases as the concentration of carbon dioxide increases, but only up to a certain point. Beyond will not increase the rate.
- Temperature – affects enzyme activity. As the temperature increases, the rate of photosynthesis increases up to a point and then starts decreasing because of denaturation of enzymes.
LIGHT AFFECTING GAS EXCHANGE
Like all living cells, aerobic respiration happens continuously in plant cells. However, photosynthesis only happens in the presence of light. This means:
At night, overall plants will release carbon dioxide
At day, overall plants will release oxygen
This can be tested using a hydrogen carbonate indicator: used to estimate the carbon dioxide concentration in water. It is used to test light intensity effecting gas exchange in aquatic plants.
ADAPTATIONS OF LEAVES
Leaves are well adapted to their function of photosynthesis. Apart from chlorophyll, leaves require sunlight, carbon dioxide and water to make food. Leaves have adapted in the following ways:
- Large surface areas - exposes a larger area to sunlight and air, easier absorption of these materials
- Thin – ensures carbon dioxide from the air diffuses quickly to the photosynthetic cells. The thinness of the leaves also helps the light to penetrate easily (to go to the cells that perform photsynthesis)
LEAF STRUCTURE
check urself
Cells that can photosynthesize (contains chlorophyll):
1. Palisade mesophyll
2. Spongy mesophyll
3. Guard cells
FUNCTIONS AND ADAPTATIONS of plant structures
- Cuticle – a waxy layer that stops water from evaporating from the leaf
- Chloroplast – site of photosynthesis, contains chlorophyll to absorb light, and enzymes
- Upper/Lower epidermis – thin and quite transparent layer of cells that lets light pass through; it protects the inner cells
- Palisade mesophyll - box-shaped cells that pack closely together; each cell has lots of chloroplasts pushed to the edges of the cell by a large vacuole so they can absorb more light; mainly for photosynthesis
- Vascular bundle – contains xylem and phloem tissues
- Guard cell – work in pairs to control opening of stomata (influenced by loss and entry of water from guard cells due to osmosis -> it changes its shape)
- Stomata - controls the diffusion of water vapour and gases in and out of the leaf
- Spongy mesophyll – site of gas exchange; cells are loosely spaced, creating air spaces
- Air spaces - allow diffusion of gases throughout the leaf
XYLEM AND PHLOEM
Xylem tissue consists of hollow tubes. It:
- transports water and dissolved mineral ions
- provides support for the plant and helping to keep it upright
Phloem tissue consists of living cells. It:
- transports sucrose
- transports amino acids
Xylem and phloem are located in vascular bundles in different positions, depending on the part of the plant. But xylem is usually bigger in diameter.
PATHWAY FROM ROOTS TO LEAVES
Root hair cells → root cortex cells → xylem → mesophyll cells
TRANSPIRATION
-> The loss of water vapour from plant leaves by evaporation of water at the surfaces of the spongy mesophyll cells into air spaces followed by the diffusion of water vapour through the stomata.
Once the water is at the leaves, it experiences two things, one after the other:
1. Evaporation at the surfaces of the spongy mesophyll cells into air spaces to form water vapour (air spaces between spongy mesophyll and a large area of cell surfaces allow rapid evaporation)
- The loss of water vapour from the leaf by diffusion through the stomata (mostly at lower epidermis so more stomata there)
The transpiration rate is affected by variations in temperature and wind speed:
- an increase in temperature results in a high rate of transpiration. The higher temperature increases evaporation and this cools the plant.
- wind is moving air. It sweeps away water vapour from the surface of leaves surface. The faster the wind speed the more evaporation from the leaves.
WILTING
If plant cells lose more water than they are gaining, they become flaccid. Flaccid cells lose their rigidity and the stems and leaves wilt (see osmosis).
Turgid cells are full of water. There is enough pressure against the cell wall to keep the plant upright.
One of the possible consequences of transpiration is wilting. This happens when the rate of transpiration is greater than the rate at which water is absorbed through the root hair cells.
The plant cells lose water, reducing their turgor pressure so they become flaccid.
TRANSLOCATion
-> the movement of sucrose and amino acids through phloem tissue from sources to sinks
The movement of substances in phloem is different from the movement of water and ions in xylem:
In xylem, the direction of movement is always from the roots to the leaves.
In phloem, the direction of movement depends on the circumstances.
When you consider the direction of translocation of a substance, you need to identify its source and its sink (always source -> sink)
A source is parts of plants that release sucrose or animo acids.
In a plant, a sink is parts of plants that use or store sucrose or animo acids. It can be:
- a region of storage
- a region of use in respiration or growth.
- a region where carbohydrates are stored as starch would be a sink for sucrose
For example, glucose is made by photosynthesis in the leaves. It is then converted into sucrose for transport around the plant. In this example, the leaves are the source of sucrose.
HUMAN BREATHING SYSTEM
-> organ system that allows the body to obtain oxygen for aerobic respiration, and to remove the carbon dioxide produced as a waste product
Nasal cavity → pharynx → larynx → trachea → lungs → bronchi → bronchioles → alveoli
*Trachea has C-shaped cartilages.
ALVEOLI AND GAS EXCHANGE
Gas exchange happens at the surface of the alveoli, allowing oxygen to diffuse from the air into blood in the capillaries, and carbon dioxide to diffuse from the blood in the capillaries into the air (external gas exchange; see difference).
Adaptations of gas exchange surfaces in humans to ensure efficient gas exchange:
- have a large surface area
- are thin
- have a good blood supply
- have good ventilation with air
COMPOSITION OF INSPIRED AND EXPIRED AIR
Inspired air is the air you breathe in, and expired air is the air you breathe out.
Gas Inspired air Expired air
Oxygen (O2) 21% 16%
Carbon dioxide (CO2) 0.04% 4%
Nitrogen (N2) 78% 78%
Water vapour Variable (lower) Always high
Explanation of change:
Less O2 -> oxygen is used by cells during aerobic respiration
More CO2 -> carbon dioxide is a waste product of respiration and must be removed from the body.
More water vapour -> because moisture evaporates from the cells of the gas exchange surface
HOW EXERCISE AFFECT BREATHING
During physical activity, muscle cells respire more to release energy: ATP.
This increases carbon dioxide production as a waste product. The rise in CO₂ levels is detected by the brain, which causes an increase in the rate and depth of breathing to remove excess CO₂ and brings in more oxygen, which is needed for aerobic respiration.
UNDERSTANDING RESPIRATION
-> the chemical reactions in cells that break down nutrient molecules to release energy for metabolism
Cellular respiration - release of energy from food molecules in living cells
(Aerobic respiration takes place in mitochondria, anaerobic in cytoplasm)
Energy released from respiration is used for:
1. Muscle contraction
2. Maintenance of constant body temperature
3. Protein synthesis
4. Cell division and growth
5. Passage of nerve impulses
6. Active transport
(Not to be confused with ventilation: breathing in and out)
AEROBIC RESPIRATION
-> chemical reactions in cells that use oxygen to break down nutrient molecules to release energy
Glucose is broken down completely and release CO2 and water as waste products.
The reaction occurs in mitochondria and relatively large amounts of energy (ATP) is released.
6O2+C6H12Og -> 6CO2 +6H2O
ANAEROBIC RESPIRATION
-> chemical reactions in cells to break down nutrient molecules to release energy without using oxygen.
Anaerobic respiration releases a lot less energy for each glucose molecule used than aerobic respiration.
During vigorous exercise, your cells cannot obtain enough oxygen for energy to be released by aerobic respiration alone.
Anaerobic respiration happens in muscle cells to provide them with sufficient energy to carry on working.
This causes the waste product, lactic acid, to build up in the muscles and blood. The word equation for anaerobic respiration there is:
glucose → lactic acid
OXYGEN DEBT
-> Build up of lactic acid in muscles and blood during vigorous exercises due to lack of oxygen.
Lactic acid is dangerous to the body and must be broken down. Your body takes several actions to remove the lactic acid:
1. Aerobic respiration in the liver to break down the lactic acid into carbon dioxide and water.
2. Continued fast heart rate to transport lactic acid in the blood from the muscles to the liver.
3. Continued deeper and faster to supply oxygen for aerobic respiration of lactic acid.
COMPOSITION OF AIR – PRACTICAL
The concentration of CO2 can be estimated using hydrogen carbonate (bicarbonate) indicator.
Carbon dioxide dissolved in water is acidic, therefore the more yellow the solution turns, the higher the concentration of CO2.
The presence of CO2 can be tested with limewater: it turns from transparent to cloudy if CO2 is present.
