Plant Physiology Quiz

Osmosis

• Water diffuses from a low concentration of solute to a high concentration of solute.
• Osmotic pressure is the pressure needed to prevent osmosis.
• Osmotic pressure increases with increasing solute concentration.

Imbibition

• Hydrophilic colloidal particles absorb liquids, causing them to swell.
• Examples include cellulose, pectin, and protoplasmic proteins.

Water Absorption in Plants

• Water enters the epidermis of roots through osmosis because the soil has a higher water concentration than the root cells.
• Water moves from cell to cell through the cytoplasm—the symplastic pathway.
• Cellulosic cell walls in root hairs absorb water by imbibition, and water then moves through the intercellular space, apoplastic pathway.

Mineral Requirements of Plants

• Principal elements include hydrogen, oxygen, and carbon.
• Macro-nutrients are magnesium, calcium, nitrogen, iron, sulfur, phosphorus, and potassium.
• Micro-nutrients are aluminum, molybdenum, manganese, zinc, boron, iodine, chlorine, and copper.
• These micro-nutrients are trace elements, needed in small quantities.
• Micro-nutrients act as co-enzymes in the body, activating enzymes.
• Mineral deficiencies can lead to disturbances in plant growth and a lack of flowers and fruit production.

Mineral Absorption Mechanism

• Minerals are absorbed from the soil by diffusion through cell walls, moving from high concentration in the soil to low concentration in the cell wall.
• Minerals are also taken up by the plant through a semi-permeable plasma membrane.
• Active transport moves molecules across the membrane against the concentration gradient, using ATP from aerobic respiration.

Active Transport vs. Selective Permeability

• An experiment using Nitella algae demonstrated the difference between active transport and selective permeability.
• The concentration of some ions in the cell sap was higher than in the surrounding water, requiring active transport to move them across the membrane.
• The unequal concentration of ions showed that the cell was selectively permeable to certain ions.

Photosynthesis in Plants

• Photosynthesis occurs mainly in green leaves and stems because they contain chloroplasts.
• Chloroplasts are structures within the cell where photosynthesis takes place.
• Chloroplasts have a double membrane, a stroma, grana, and lamellae.
• Lamellae increase surface area for absorbing light.

Digestion

• The oral cavity is made up of teeth, a tongue, and salivary glands.
• Teeth are distinguished by their shape and function, allowing for cutting, tearing, crushing, and grinding food.
• The tongue is responsible for tasting and moving food in the mouth.
• Salivary glands secrete saliva, which lubricates food, aids in swallowing, and initiates the breakdown of starch by salivary amylase (ptyalin).

Pharynx

• The pharynx is a passageway for both food and air.
• Swallowing is a reflex action triggered by the presence of food in the throat.
• The epiglottis covers the trachea when swallowing, preventing food from entering.

Oesophagus

• This 25cm tube extends from the neck to the stomach through the chest cavity.
• Mucus glands help with the movement of food down the oesophagus.
• Circular muscles responsible for peristalsis, a series of contractions and relaxations that move food to the stomach.
• The oesophagus does not have a digestive function.

Large Intestine and Defecation

• Undigested food passes from the small intestine to the large intestine.
• Water and mineral absorption occur in the large intestine due to its convolutions.
• Undigested food becomes semi-solid in the large intestine, where bacteria decompose it.
• Mucus, contraction of the rectum, and relaxation of the anal sphincter muscles facilitate the expulsion of feces.

Enzyme Scheme

• Ptyalin (salivary amylase) breaks down starch in the mouth.
• Amylase (pancreatic amylase) breaks down starch in the duodenum.
• Maltose is broken down by maltase.
• Sucrose is broken down by sucrase.
• Lactose is broken down by lactase.
• Lipase is involved in the breakdown of emulsified fats and oils.