Topic 3

Cellular Organization: basic unit of an organism

cell; cells of similar design/function grouped together make tissue; tissues working together make organs; organs working together make organ systems; organ systems make the organism

What are the three main organs of a plant?

leaves, stems, and roots

What is the main job of the leaf?

make food through photosynthesis and gas exchange

What is the main job of the stem?

transport water and nutrients throughout the plant

What is the main job of the roots?

uptake of water and nutrients

What is the chemical equation for photosynthesis?

6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂

What organelle is responsible for photosynthesis?

chloroplast

What pigment traps light energy in chloroplasts?

chlorophyll

What is cellular respiration?

the process that converts glucose into usable energy (ATP) in the mitochondria

What is the opposite reaction to photosynthesis?

cellular respiration

What are four advantages of being multicellular?

larger size, variety of specialized cells, ability to thrive in a range of environments, and organization of cells

What are stomata?

tiny openings in the leaf surface that allow gases to diffuse in and out

What is transpiration?

the evaporation of water from the leaf's stomata

What do guard cells do?

control the opening and closing of stomata to prevent dehydration

When do stomata typically open?

during the day (high photosynthesis, high transpiration)

When do stomata typically close?

during the night or in hot/dry conditions to prevent water loss

What causes stomata to open?

water flows into guard cells by osmosis, causing them to swell (turgor pressure), which opens the pore

What causes stomata to close?

water leaves guard cells, causing them to deflate, which closes the pore

What is turgor pressure?

high water pressure inside a cell that pushes the cell membrane against the cell wall, keeping cells firm

What are lenticels?

pores on stems that allow for gas exchange

How does CO₂ enter the leaf for photosynthesis?

CO₂ diffuses through stomata and into air spaces between cells, then into palisade cells down a concentration gradient

What is the xylem?

vascular tissue that transports water from roots to leaves

What is the phloem?

vascular tissue that transports sugar (glucose) from leaves to the rest of the plant

What is xylem sap?

water and minerals gathered at the root xylem, carried upwards to leaves

What is phloem sap?

sugar solution (sugars, minerals, nutrients) that flows down the phloem to neighboring cells

How do water and minerals enter the roots?

minerals enter via facilitated diffusion or active transport; water enters root hairs through osmosis

Why are root hairs important?

they increase surface area for maximum water and mineral absorption

How do sugars move into the phloem?

sugars, minerals, and nutrients are pumped into the phloem through active transport

Why does water follow sugar into the phloem?

the sugar solution is hypertonic compared to surrounding cells, so water enters by osmosis

What is the function of companion cells?

they act as "personal assistants" to phloem cells, helping them transport sap efficiently

What is a tropism?

a plant's growth response to a stimulus in the environment

What is phototropism?

growth of a plant toward a light source (cells on the shaded side elongate)

What hormone is responsible for phototropism?

auxin (stimulates cell elongation in stems)

What is gravitropism?

response to gravity (stems grow up — negative; roots grow down — positive)

How does auxin affect roots and stems differently?

in stems, auxin stimulates growth; in roots, auxin inhibits growth

What is a nastic response?

a non-directional response to touch (e.g., Venus Fly Trap, Mimosa)

What is the formula for photosynthesis?

6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂

What gases are exchanged through stomata?

CO₂, O₂, and H₂O vapor

Why do plants in hot dry climates open stomata at night?

to gather CO₂ and store it for photosynthesis during the day, reducing water loss

What is diffusion in the context of gas exchange?

movement of gases from high concentration to low concentration (passive transport)

What is osmosis?

diffusion of water across a selectively permeable membrane from high water concentration to low water concentration

What is active transport?

movement of molecules from low concentration to high concentration, requiring energy

What is the main function of the phloem?

transport sugars from leaves (source) to the rest of the plant (sink)

What is the main function of the xylem?

transport water and minerals from roots to leaves

Where does photosynthesis occur in the leaf?

in the chloroplasts of palisade tissue cells

What is the advantage of having air spaces between leaf cells?

allows gases (CO₂, O₂) to circulate freely

What is the relationship between photosynthesis and cellular respiration in plants?

photosynthesis consumes CO₂ and H₂O and releases O₂; cellular respiration consumes O₂ and produces CO₂ and H₂O

What happens if a plant loses too much water?

stomata close, and the plant may wilt or dry out