Cell Biology Flashcards
What are microscopes used for?
To see objects that cannot be seen with the naked eye
When did purposeful magnification first appear?
Before 2500 BCE
In which century were lenses first invented?
12-13th century
Fill in the blank: Microscopes are instruments that are used to see objects that cannot be seen with the _______.
naked eye
True or False: Microscopes have been in use since before 500 CE.
True
Who are credited with creating the forerunner of the compound microscope?
Zaccharias Janssen and Hans Janssen
They experimented with multiple lenses placed in a tube.
In what year did Hooke publish his book Micrographia?
1665
This book described his observations made with a microscope.
What did Hooke observe through the microscope that led him to name them ‘cells’?
Pores/compartments in cork
His observations were made on slivers of cork.
Who is known as the ‘Father of Microbiology’?
Van Leeuwenhoek
He built numerous simple microscopes and discovered many microorganisms.
What type of microscopes did Van Leeuwenhoek build?
Simple microscopes with single lenses
He achieved magnifications up to 270X.
What did Van Leeuwenhoek study using his microscopes?
Bacteria, yeast, plants, and small organisms in pond water
His studies included a variety of small life forms.
Fill in the blank: The early compound microscope was developed in _______.
1595
This development involved the use of multiple lenses.
True or False: Hooke was the first to observe cells.
True
Hooke’s observations in cork led to the naming of cells.
Who first used specific dyes to stain specific structures in cells?
Joseph von Gerlach
He did this in 1858 and recognized the importance of staining.
What significant contribution did Oskar Heimstädt make in 1911?
Constructed the first successful fluorescence microscope
This microscope uses a high-intensity light source to excite fluorescent molecules.
What is the principle behind fluorescence microscopy?
It uses a high-intensity light source to excite a fluorescent molecule, which emits lower energy light of a longer wavelength
This emitted light produces the magnified image.
In what year was the first electron microscope invented?
1931
It was co-invented by German scientists Max Knott and Ernst Ruska.
What does an electron microscope use to illuminate a specimen?
An electron beam
This allows it to produce a magnified image.
What are the two main types of electron microscopes?
- TEM (transmission electron microscopes)
- SEM (scanning electron microscopes)
Each type has distinct imaging capabilities.
What type of images do TEM microscopes obtain?
2D images
They can magnify up to ~1,000,000X.
What type of images do SEM microscopes obtain?
3D images of surface structures
They can magnify up to ~100,000X.
Fill in the blank: The first successful fluorescence microscope was constructed by _______.
Oskar Heimstädt
Who first used specific dyes to stain specific structures in cells?
Joseph von Gerlach
He did this in 1858 and recognized the importance of staining.
What significant contribution did Oskar Heimstädt make in 1911?
Constructed the first successful fluorescence microscope
This microscope uses a high-intensity light source to excite fluorescent molecules.
What is the principle behind fluorescence microscopy?
It uses a high-intensity light source to excite a fluorescent molecule, which emits lower energy light of a longer wavelength
This emitted light produces the magnified image.
In what year was the first electron microscope invented?
1931
It was co-invented by German scientists Max Knott and Ernst Ruska.
What does an electron microscope use to illuminate a specimen?
An electron beam
This allows it to produce a magnified image.
What are the two main types of electron microscopes?
- TEM (transmission electron microscopes)
- SEM (scanning electron microscopes)
Each type has distinct imaging capabilities.
What type of images do TEM microscopes obtain?
2D images
They can magnify up to ~1,000,000X.
What type of images do SEM microscopes obtain?
3D images of surface structures
They can magnify up to ~100,000X.
Fill in the blank: The first successful fluorescence microscope was constructed by _______.
Oskar Heimstädt
What technology allows microscopes to view things smaller than the wave size of light?
Super-resolution light microscopy
This technology has been developed since 2000.
What new insights can super-resolution light microscopy provide?
Understanding of cell biology
It allows for visualization of cells at a tiny scale.
What are the capabilities of super-resolution light microscopy?
Imaging in all three dimensions and within living cells
These capabilities are developing rapidly.
What is the most commonly used microscope?
Compound light microscope
What is the upper lens of the microscope called?
Eyepiece
What holds the lenses of the microscope?
Body tube
What part of the microscope carries the objective lenses?
Revolving nosepiece
What is the lower lens of the microscope that is movable for different magnifications?
Objective lens
What holds the slide in place on the microscope?
Stage clips
What part of the microscope regulates the amount of light shining on the object?
Diaphragm
What provides light that shines through the opening and the mounted object to the eye?
Light source
What is the handle of the microscope called?
Arm
Where is the slide clipped to be observed in a microscope?
Stage
What knob moves the tube/stage with large movements to bring the object into focus?
Coarse adjustment knob
What knob moves the tube/stage with fine movements for final focus?
Fine adjustment knob
What part of the microscope ensures it stands steady?
Base
What does the original cell theory state?
The cell is the basic structural and functional unit of living organisms and all cells come from other cells.
This theory was established by Matthias Schleiden and Theodor Schwann in 1839.
Who are credited with establishing the cell theory?
Matthias Schleiden and Theodor Schwann.
They established the theory in 1839.
What did Matthias Schleiden propose about cells?
All plant tissues are composed of cells.
This foundational belief was proposed between 1838-1839.
What conclusion did Theodor Schwann make regarding cells?
All animal tissues are made of cells.
Schwann’s conclusion was integral to the development of cell theory.
What are the two foundational statements of the original cell theory?
- All living organisms consist of one or more cells
- The cell is the basic unit of life
These statements were blended by Schwann into the cell theory.
Who added the third part of the original cell theory and what was it?
Rudolf Virchow proposed that cells only arise from other cells in 1855.
This conclusion was based on his observations of mitosis.
What does the modern version of the cell theory include?
- Energy flows within cells
- Hereditary information is passed from cell to cell
- Cells are made of the same basic chemical components
These ideas reflect advancements in biological knowledge since the mid-1800s.
Fill in the blank: The cell is the _______ unit of life.
basic
This is a key concept in the original cell theory.
True or False: All living organisms consist of only one cell.
False
The original cell theory states that organisms can consist of one or more cells.
What are the two main components that all cells consist of?
Cytoplasm and a cell membrane
These components are essential for the cell’s structure and function.
What is an organelle?
A subcellular structure that has one or more specific jobs to perform in the cell
Organelles function similarly to organs in the body.
What type of cells lack a nucleus and other membrane-bound organelles?
Prokaryotic cells
Examples include bacteria.
What type of cells contain a nucleus and other membrane-bound organelles?
Eukaryotic cells
Examples include plants and animals.
Fill in the blank: Cells without a nucleus and other membrane surrounded organelles are called _______.
Prokaryotic cells
Fill in the blank: Cells with a nucleus and other membrane surrounded organelles are called _______.
Eukaryotic cells
True or False: All cells have a nucleus.
False
Prokaryotic cells do not have a nucleus.
What is the primary difference between prokaryotic and eukaryotic cells?
Presence of a nucleus and membrane-bound organelles
Prokaryotic cells lack these features.
What is the function of the cell membrane?
Regulates what enters and exits the cell
The cell membrane is a selectively permeable barrier that protects the cell’s internal environment.
What organelle contains the cell’s genetic material?
Nucleus
The nucleus houses DNA and is often referred to as the control center of the cell.
What is cytoplasm?
The gel-like substance within the cell membrane
Cytoplasm contains all organelles and is the site of many metabolic processes.
What is the primary role of mitochondria?
Energy production through cellular respiration
Mitochondria are often called the powerhouse of the cell.
What are ribosomes responsible for?
Protein synthesis
Ribosomes can be found floating freely in the cytoplasm or attached to the endoplasmic reticulum.
What is the function of the endoplasmic reticulum?
Protein and lipid synthesis, and transport
The endoplasmic reticulum can be rough (with ribosomes) or smooth (without ribosomes).
What does the Golgi body do?
Modifies, sorts, and packages proteins and lipids
The Golgi apparatus plays a key role in processing and shipping cellular products.
What are vacuoles?
Storage organelles in the cell
Vacuoles can store nutrients, waste products, or other materials.
Which cells contain a cell wall?
Plant cells
The cell wall provides structural support and protection.
What is the main function of chloroplasts?
Photosynthesis
Chloroplasts contain chlorophyll and convert sunlight into chemical energy.
What is the cell membrane?
A very thin, living boundary of the cell
The cell membrane is crucial for maintaining the integrity of the cell.
What model describes the structure of the cell membrane?
Fluid Mosaic Model
The Fluid Mosaic Model explains how the cell membrane is composed of various components that move fluidly.
What are the main components of the cell membrane?
A double layer of phospholipid molecules with large proteins embedded
This arrangement allows for flexibility and functionality within the membrane.
What are the two parts of a phospholipid molecule?
Phosphate head and fatty acid tail
The phosphate head is hydrophilic, while the fatty acid tail is hydrophobic.
What does hydrophilic mean?
Attracted to water
Hydrophilic substances tend to interact well with water.
What does hydrophobic mean?
Repelled by water
Hydrophobic substances do not mix well with water.
Describe the movement of phospholipids and proteins in the cell membrane.
They constantly move around like objects floating on the surface of a lake
This movement is essential for the dynamic function of the membrane.
What is the function of the cell membrane?
Protects and encloses the cell; selectively permeable
The selective permeability allows the cell to control its internal environment.
What does selectively permeable mean?
Allows and controls the movement of substances into and out of the cell
This property is vital for maintaining homeostasis.
What are microvilli?
Tiny cell membrane projections that increase surface area
Microvilli are important for absorption and secretion processes in some animal cells.
What does hydrophilic mean?
‘Attracted’ to water
Hydrophilic substances tend to dissolve in water or interact favorably with it.
What does hydrophobic mean?
‘Repelled’ by water
Hydrophobic substances do not mix well with water and often aggregate in aqueous environments.
What is cytoplasm?
A jelly-like, colloidal solution in a cell that appears grey due to organelles and suspended substances.
The cytoplasm consists of cytosol (liquid component) and suspended proteins and organelles.
What is the liquid component of cytoplasm called?
Cytosol
The cytosol is the liquid part of the cytoplasm where various substances are suspended.
What is the solid component of cytoplasm comprised of?
Suspended proteins and organelles
These components contribute to the colloidal nature of the cytoplasm.
What structural element is found within the cytoplasm?
Cell cytoskeleton
The cytoskeleton is a network of protein fibres and microtubules that helps maintain cell shape.
What processes take place in the cytoplasm?
Metabolism
Metabolism includes all chemical processes necessary for the survival of the organism.
What are the functions of the cytoplasm?
Stores substances, gives cell shape, facilitates circulation of substances
The movement of the cytoplasm aids in the distribution of materials within the cell.
Fill in the blank: The cytoplasm is a _______ solution.
colloidal
A colloidal solution consists of microscopically dispersed insoluble particles suspended in a liquid.
True or False: The cytoplasm is only responsible for storing substances.
False
The cytoplasm also plays a crucial role in metabolism and maintaining cell shape.
What types of organisms have cell wall structures?
Bacteria, some protists, fungi, and plants
Cell walls are a common feature in various life forms, providing structural support.
What is the primary component of the primary cell wall in plants?
Cellulose
Cellulose allows the primary cell wall to stretch as the cell grows.
What substance makes up the middle lamella in plant cell walls?
Pectin
Pectin acts like glue, connecting adjacent plant cells.
What is the composition of the secondary cell wall in older plant cells?
Cellulose and lignin
The secondary cell wall is thicker, inelastic, and provides additional strength.
What are pits in the primary and secondary cell wall associated with?
Plasmodesmata
Plasmodesmata are cytoplasmic threads that extend between adjacent cells, facilitating communication.
True or False: A cell wall is a living cell component.
False
Cell walls are considered non-living structures.
What are the main functions of the cell wall?
- Support structure for cells
- Protect cells
- Provide rigidity (shape and strength)
- Allow substances to move through
The cell wall plays a crucial role in maintaining cell integrity and regulating transport.
Fill in the blank: The primary cell wall can _______ as the cell grows.
stretch
This flexibility is important for cell growth and development.
What role do plasmodesmata play in plant cells?
Transport substances between adjacent cells
They facilitate intercellular communication and nutrient exchange.
What is a nucleus?
A round or oval organelle in the cytoplasm
It consists of a nuclear membrane with pores.
What are the main components found inside the nucleus?
Nucleoplasm, chromatin network, and nucleolus
Chromatin network consists of DNA and proteins.
What is the function of the nucleus?
Controls all activities of the cell
The DNA contains the code to make all the cell’s proteins.
What role does DNA play in the nucleus?
Carries hereditary characteristics and is replicated for cell division
This replication is crucial for passing genetic information to the next generation of cells.
Where is DNA found in prokaryotic cells?
In the cytoplasm
Unlike eukaryotic cells, prokaryotes do not have a defined nucleus.
Fill in the blank: The nucleus consists of a nuclear membrane with _______.
pores
True or False: The nucleolus is a lighter body found inside the nucleus.
False
The nucleolus is described as a darker body.
What does the chromatin network in the nucleus consist of?
DNA and proteins
Fill in the blank: The nucleoplasm is found inside the _______.
nucleus
What is a nucleus?
A round or oval organelle in the cytoplasm
It consists of a nuclear membrane with pores.
What are the main components found inside the nucleus?
Nucleoplasm, chromatin network, and nucleolus
Chromatin network consists of DNA and proteins.
What is the function of the nucleus?
Controls all activities of the cell
The DNA contains the code to make all the cell’s proteins.
What role does DNA play in the nucleus?
Carries hereditary characteristics and is replicated for cell division
This replication is crucial for passing genetic information to the next generation of cells.
Where is DNA found in prokaryotic cells?
In the cytoplasm
Unlike eukaryotic cells, prokaryotes do not have a defined nucleus.
Fill in the blank: The nucleus consists of a nuclear membrane with _______.
pores
True or False: The nucleolus is a lighter body found inside the nucleus.
False
The nucleolus is described as a darker body.
What does the chromatin network in the nucleus consist of?
DNA and proteins
Fill in the blank: The nucleoplasm is found inside the _______.
nucleus
What are ribosomes?
Tiny, spherical structures found in all cells
Ribosomes are essential for protein synthesis.
What are ribosomes made of?
RNA and proteins
This composition is crucial for their function in protein synthesis.
Where are ribosomes located?
On the rough endoplasmic reticulum, in chloroplasts and mitochondria, and free in the cytoplasm
Their locations are critical for various cellular functions.
What is the primary function of ribosomes?
To enable protein synthesis
Ribosomes are the sites where proteins are made from amino acids.
What is the Endoplasmic Reticulum (ER)?
A membranous network that forms a continuous system of canals throughout the cytoplasm.
How is the Endoplasmic Reticulum connected to other cellular structures?
It is connected to the cell and nuclear membrane.
What distinguishes Rough ER from Smooth ER?
Rough ER has ribosomes on its surface; Smooth ER does not.
What is the primary function of Rough ER?
Protein synthesis and folding.
What is the primary function of Smooth ER?
Synthesis of lipids.
What additional role does the Endoplasmic Reticulum play in the cell?
It assists in transporting substances around the cytoplasm.
The Endoplasmic Reticulum increases what aspect of the cell?
The internal surface area of the cell.
What is the structure of the Golgi body?
Stacks of hollow, flat membrane sacs known as cisternae
The Golgi body is typically located near the nucleus of the cell.
What are the primary functions of the Golgi body?
Produces and processes secretions and prepares proteins for transport
An example of a secretion produced by the Golgi body is mucus.
True or False: The Golgi body is primarily involved in energy production.
False
The Golgi body is involved in processing and transporting proteins, not energy production.
Fill in the blank: The Golgi body consists of stacks of hollow, flat membrane sacs known as _______.
cisternae
Cisternae are the structural components of the Golgi body.
Where is the Golgi body typically located within the cell?
Near the nucleus
This location allows the Golgi body to efficiently process proteins synthesized in the rough endoplasmic reticulum.
What are mitochondria?
Organelles found in eukaryotic cells (including plants and animals)
What shape are mitochondria typically?
Small and oval-shaped
What type of membrane do mitochondria have?
Double membrane
What are the finger-like folds in the inner membrane of mitochondria called?
Cristae
What is the purpose of the cristae in mitochondria?
To increase the internal surface area for more chemical reactions
What is the fluid inside mitochondria called?
Matrix
What does the matrix contain?
Ribosomes and enzymes
Do mitochondria have their own DNA?
Yes
What process takes place in mitochondria?
Cellular respiration
What energy is released from glucose in the presence of oxygen?
ATP
What is ATP?
The energy carrier in cells
Which type of cells contain more mitochondria?
More active cells (e.g., muscle cells)
What are chloroplasts?
Chloroplasts are green plastid organelles found in eukaryotic algae and plants.
Where are chloroplasts mainly found in plants?
In the leaf cells.
What is the primary function of chloroplasts?
To perform photosynthesis and produce glucose.
What surrounds the chloroplast?
A double membrane.
What is the fluid part inside a chloroplast called?
The stroma.
What structures are found within the stroma of a chloroplast?
Double-walled membranes called lamellae, which form the grana.
What are grana composed of?
Structural units called thylakoids.
What do thylakoids contain?
Chlorophyll.
Do chloroplasts have their own DNA?
Yes, chloroplasts have their own DNA and ribosomes.
What do autotrophic eukaryotes produce through photosynthesis?
Glucose.
What is excess glucose stored as in plants?
Starch.
True or False: Chloroplasts are only found in animal cells.
False.
Fill in the blank: Chloroplasts are essential for making glucose through _______.
photosynthesis.
What are plastids with different colour pigments called?
Chromoplasts
Chromoplasts are responsible for the various colors found in flowers, leaves, and fruits.
What are colourless plastids called?
Leucoplasts
Leucoplasts do not have pigmentation and serve different functions.
What is the primary function of chromoplasts?
To give different colours to flowers, leaves, and fruit
Chromoplasts contain pigments other than green, contributing to plant coloration.
What do leucoplasts primarily store?
Food as starch, lipids, and proteins
Leucoplasts are specialized for storage functions in plants.
What are vacuoles in plant cells?
Large fluid-filled cavities in the cytoplasm surrounded by a semi-permeable membrane called the tonoplast
The fluid inside is known as cell sap.
In which type of cells are vacuoles large and prominent?
In plant cells
In animal cells, vacuoles are small or absent.
What is the function of the large central vacuoles in plants?
Create turgor pressure, provide rigidity, and store water and nutrients
Turgor pressure helps prevent wilting.
What type of vacuoles regulate water balance?
Contractile vacuoles
These vacuoles are important for maintaining osmotic balance.
What do food vacuoles do?
Digest and store food
They play a crucial role in nutrient absorption.
What is the function of vesicles?
Transport substances around and out of the cell
Vesicles are essential for cellular transport processes.
What do lysosomes release to aid in digestion?
Enzymes
This function is primarily observed in animal cells.
True or False: Vacuoles are absent in animal cells.
False
While vacuoles are small or less prominent in animal cells, they are not entirely absent.
Fill in the blank: The fluid inside vacuoles is called _______.
cell sap
Cell sap contains various substances, including nutrients and waste products.
List the types of vacuoles mentioned.
- Lysosomes
- Vesicles
- Contractile vacuoles
- Food vacuoles
Each type has distinct functions within the cell.
What are centrosomes?
Centrosomes are found in animal cells and consist of two small cylinder-shaped structures called centrioles.
What shape are centrioles?
Centrioles are cylinder-shaped structures.
How do centrioles in a centrosome relate to each other?
Centrioles lie close together at a right angle.
What are the main components of centrioles?
Centrioles consist of fibrils and microtubules.
What role do centrioles play in animal cells?
Centrioles play a role in the formation of the spindle during cell division.
What type of organisms are both plants and animals classified as?
Eukaryotes
Name three organelles common to both plant and animal cells.
- Cell membrane
- Cytoplasm
- Nucleus
What organelle is responsible for energy production in both plant and animal cells?
Mitochondria
Which unique structure is found in plant cells but not in animal cells?
Cell wall
Fill in the blank: Plant cells have __________ that give them a fixed shape.
cell walls
What type of vacuoles do plant cells typically have?
Large permanent vacuoles
True or False: Animal cells have plastids.
False
Which organelle is found in animal cells but not in plant cells?
Centrosomes
Describe the typical shape of animal cells.
Irregular shape
List two organelles found in both plant and animal cells.
- Ribosomes
- Golgi body
What is necessary for cells to acquire oxygen and nutrients?
The movement of substances across cell membranes
This movement also allows cells to excrete waste products and control the concentration of required substances.
What are the key processes through which movement across cell membranes occurs?
- Diffusion
- Osmosis
- Active transport
These processes help in the movement of substances necessary for cellular functions.
What is a concentration gradient?
Differences between high and low concentrations of the same molecules in different areas
Concentration gradients drive the movement of molecules.
What is the direction of spontaneous movement of molecules in a concentration gradient?
From high concentration to low concentration until equilibrium is reached
This movement occurs naturally due to the kinetic energy of each particle.
What is the state of equilibrium in the context of diffusion?
Molecules are equally distributed throughout the medium
Equilibrium signifies that there is no net movement of molecules.
What type of process is diffusion?
Passive process
This means it does not require a specific input of energy.
Fill in the blank: The movement of molecules occurs because each particle has _______.
kinetic energy
Kinetic energy allows particles to move spontaneously.
What is passive transport?
The spontaneous movement of molecules across a membrane from high concentration to low concentration without energy input from the cell.
Examples include carbon dioxide, oxygen, water, and other small molecules that can dissolve in the lipid bilayer.
What type of molecules are typically moved by passive transport?
Small molecules that can dissolve in the lipid bilayer, such as:
* Carbon dioxide
* Oxygen
* Water
These molecules move from areas of higher concentration to areas of lower concentration.
What is facilitated transport?
The spontaneous movement of molecules across a cell’s membrane via specific membrane proteins without energy input.
This process involves diffusion through channel proteins.
What types of substances are commonly moved by facilitated transport?
Larger molecules, such as:
* Glucose
Facilitated transport utilizes membrane proteins to assist the movement of these larger molecules across the membrane.
True or False: Passive transport requires energy input from the cell.
False
Passive transport occurs spontaneously and does not require energy.
Fill in the blank: Facilitated transport involves the movement of molecules through _______.
[specific membrane proteins]
These proteins can include channel proteins that assist in the diffusion process.
What is osmosis?
The movement of water across a membrane
Define osmosis in detail.
The movement of water molecules from an area of high water potential, through a selectively permeable membrane, to an area of low water potential, until equilibrium is reached
What is high water potential?
Pure water or a weak/dilute solution (called hypotonic)
What is low water potential?
A strong/concentrated solution (called hypertonic)
What is a selectively permeable membrane?
A membrane with tiny pores that allow only small molecules to pass, but not big ones
What does equilibrium in osmosis refer to?
The solution concentrations on either side of the membrane are equal (called isotonic)
Fill in the blank: Osmosis is the movement of water from an area of high water potential to an area of _______.
low water potential
True or False: A hypotonic solution has a high water potential.
True
True or False: An isotonic solution has unequal concentrations on either side of a membrane.
False
What process allows plants to take up water from the soil?
Osmosis
Osmosis is the movement of water across a semi-permeable membrane from an area of low solute concentration to an area of high solute concentration.
How does water move through a plant after being absorbed by the roots?
Water moves along the cells of the root into the xylem and to the leaves
This movement is essential for photosynthesis and maintaining plant structure.
What effect does osmosis have on plant cells?
Makes plant cells turgid
Turgidity is important for maintaining the structure and rigidity of the plant.
What happens to the vacuole in plant cells during osmosis?
The vacuole swells and pushes against the cell wall
This pressure helps maintain the cell’s shape and prevents wilting.
What occurs when plant cells lack water?
Cells become flaccid and the plant wilts
Flaccidity is a sign of water deficiency in plants.
What is plasmolysis in plant cells?
Cytoplasm peels away from the cell wall due to lack of water
Plasmolysis can lead to cell death if not resolved.
What can happen to animal cells if they take in too much water by osmosis?
They might burst
This is known as cytolysis and occurs when the osmotic pressure is too high.
How do certain organelles in animal cells respond to excess water?
They pump out water if the cell is too full
This mechanism helps maintain osmotic balance within the cell.
Fill in the blank: Water moves through the plant from a _______ to _______ water potential.
high to low
This movement is driven by the difference in water potential gradients.
What is active transport?
The movement of a substance across a membrane against the concentration gradient that requires energy from respiration in the form of ATP.
What energy source is needed for active transport?
Adenosine triphosphate (ATP).
Name one example of active transport in plants.
Absorption of ions (mineral salts) from very diluted soil solutions.
Name one example of active transport in animals.
Absorption of sugar from low concentrations in the small intestine into the blood.
In which organ does active transport reabsorb sugar back into the blood?
The kidneys.
Fill in the blank: Active transport requires energy from _______.
respiration.
True or False: Active transport moves substances down their concentration gradient.
False.
List two functions of active transport.
- Absorbing ions in plants
- Reabsorbing sugar in animals
