B3 - Living together - Food and Ecosystems Flashcards
What are enzymes?
Biological catalysts that the rate of a
chemical reaction go faster without being
permanently altered themselves.
What is the active site of an enzyme?
The region of an enzyme in which a
substrate molecule binds and the
reaction takes place.
Why are enzymes described as having a
‘high specificity’ for their substrate?
Only substrates with a specific,
complementary shape can fit into an
enzyme’s active site.
Describe the ‘lock and key’ model
- The active site of the enzyme and the substrate
come into contact - Substrate binds, enzyme-substrate complex forms
- Substrate converted to products
- Products released from the active site. The active
site is now free to bind to another substrate.
What factors affect the rate of an
enzyme-controlled reaction?
● Temperature
● pH
● Substrate concentration
Explain how increasing temperature
initially affects the rate of an
enzyme-controlled reaction
● As temperature increases molecules have more KE
● Movement of molecules increases
● Probability of a successful collision increases
● More enzyme-substrate complexes form
● Rate of reaction increases
Explain how increasing temperature
above the optimum affects the rate of an
enzyme-controlled reaction
● Temperature increases above the optimum
● Increased vibrations break bonds in enzyme’s structure
● Active site changes shape, the enzyme is denatured
● No more enzyme-substrate complexes can form
● Rate of reaction decreases
Explain how pH affects the rate of an
enzyme-controlled reaction
● Enzymes have an optimum pH
● pH shifts from the optimum
● Bonds in the enzyme’s structure are altered
● Active site changes shape, enzyme is denatured
● Rate of reaction decreases
Explain how substrate concentration
affects the rate of an enzyme-controlled
reaction
● Substrate concentration increases
● Number of substrate molecules in the same volume increases
● Probability of a successful collision increases
● More enzyme-substrate complexes form
● Rate of reaction increases
● Once all active sites become full, the rate of reaction plateaus
What is photosynthesis?
A chemical reaction that takes place inside photosynthetic organisms (e.g. plants, algae) converting light energy into chemical energy
Write the word equation for
photosynthesis
carbon dioxide + water → glucose + oxygen
Write the symbol equation for
photosynthesis
6CO2+ 6H2O → C6H12O6+ 6O2
Why is photosynthesis important?
Photosynthesis produces glucose which has a wide range of uses:
● Used in respiration to release energy
● Converted to starch and stored - starch can be broken down to glucose when the plant requires energy
● Used to make a wide range of organic molecules such as lipids, proteins and other sugars which are used for growth
Where does photosynthesis take place?
Within chloroplasts
What type of reaction is photosynthesis?
An endothermic reaction that takes in
energy (in the form of light)
What is chlorophyll?
A pigment found in chloroplasts that
absorbs light
Describe the two main stages of
photosynthesis
- Chlorophyll absorbs light energy which is used to split water into oxygen gas (a waste product) and hydrogen ions
- Carbon dioxide combines with hydrogen ions to form glucose
What does the first stage of
photosynthesis require?
Light energy
Water, H2O
What are the products of the first stage
of photosynthesis?
Oxygen gas, O2
(O2 is a waste product and is released into the atmosphere)
Hydrogen ions, H+
What does the second stage of
photosynthesis require?
Carbon dioxide gas, CO2
Hydrogen ions, H+
What is produced in the second stage of
photosynthesis?
Glucose, C6H12O6
What factors affect the rate of
photosynthesis?
● Temperature
● Light intensity
● Carbon dioxide concentration
What is a limiting factor?
A variable that limits the rate of a
particular reaction
Explain how temperature affects the rate
of photosynthesis
● Higher temperatures provide more KE for enzymes involved in photosynthesis so the rate increases as temperature rises
● The optimum temperature is usually 25°C
● If the temperature becomes too high (around 45°C) enzymes become denatured and the rate of photosynthesis decreases
Explain how light intensity affects the
rate of photosynthesis
As light intensity increases, the rate of
photosynthesis increases until another
factor (e.g. temperature) becomes
limiting.
How can the effect of light intensity on
the rate of photosynthesis be measured
in the lab?
● Using a light meter
● Using the inverse square law
Why does the rate of photosynthesis
decrease as the distance from a light
source increases?
Light intensity is inversely proportional to the
square of the distance from the light source.
Thus, as the distance increases, light intensity
decreases and the rate of photosynthesis
decreases.
Explain how carbon dioxide
concentration affects the rate of
photosynthesis
As carbon dioxide concentration
increases, the rate of photosynthesis
increases until another factor (e.g. light
intensity) becomes limiting.
What is simple diffusion?
The net movement of molecules from an
area of high concentration to an area of
low concentration down a concentration
gradient
Define osmosis
The net movement of water molecules from
an area of high water concentration to an
area of low water concentration across a
partially permeable membrane
What is active transport?
The movement of molecules across a cell
membrane from an area of low concentration
to an area of high concentration, against the
concentration gradient, using energy
By what process do substances enter
and leave single-celled organisms?
Simple diffusion
Why can’t multicellular organisms rely on
simple diffusion alone?
● Small surface area to volume ratio
● Several layers of tissue too deep to
diffuse through
Why must carbon dioxide be
transported into plants and oxygen be
transported out?
Carbon dioxide is required for
photosynthesis.
Oxygen is a by-product of photosynthesis
so it is released.
How do gases such as oxygen and
carbon dioxide move into and out of
plants?
● Diffuse through stomata on the lower surface of the
leaf and through air-filled spaces within the leaf
● Move between cells via simple diffusion across
partially permeable cell membranes
Why do plants require water?
● Photosynthesis
● Maintenance of structure (turgidity)
● Cooling effect
Why do plants require mineral ions?
For growth e.g. nitrates are required to
produce proteins
How are water and minerals transported
into plants?
● Lower concentration of water in root hair cells than in the soil. Water diffuses down its concentration gradient into root hair cells by osmosis.
● Lower concentration of mineral ions in the soil than in the root. Root hair cells take up mineral ions by active
transport.
Outline how root hair cells are adapted
for the absorption of water and minerals
Plant roots are composed of millions of root hair cells which have:
● Long hairs that extend from the cell body, increasing the surface area for absorption
● Many mitochondria which produce ATP for active transport of mineral ions
Name the two plant transport tissues
Xylem
Phloem
What is the function of the xylem?
Transports water and minerals up the
plant, from the roots to the leaves via the
transpiration stream
Describe how the xylem is adapted to
its function
● Composed of dead cells laid end-to-end to form a long, hollow, continuous column
● No end walls which provides little resistance to the
passage of water
● A thick cell wall, composed of cellulose, is strengthened with lignin to provide support
