Organisms exchange substances

• Why do single-celled organisms not require specialized exchange surfaces?

  Short diffusion distance
• Multicellular organisms have a higher surface area to volume ratio compared to single-celled organisms.
• Why do insects not require a transport system for oxygen?

  Oxygen moves directly to tissues
• Plants use stomata in their leaves to allow gases to enter and exit.
• Digestion is the hydrolysis of large biological molecules into smaller molecules.
• Match the enzyme with the carbohydrate it digests:

  Amylase ↔️ Larger carbohydrates

  Maltase ↔️ Monosaccharides

  Sucrase ↔️ Sucrose

  Lactase ↔️ Lactose
• Which enzyme digests lipids?

  Lipase
• Bile salts emulsify lipids to increase their surface area for digestion.
• What type of peptidase hydrolyses peptide bonds in the middle of a polypeptide?

  Endopeptidase
• Amino acids are absorbed by facilitated diffusion in the ileum.
• Haemoglobin consists of two alpha helices and two beta polypeptide chains.
• What part of haemoglobin does oxygen bind to?

  Haem group
• The affinity of oxygen for haemoglobin depends on the partial pressure of oxygen.
• Oxygen binds to haemoglobin tightly in the lungs where the partial pressure of oxygen is high.
• What type of curve illustrates the change in haemoglobin saturation as partial pressure changes?

  Dissociation curve
• Oxygen binds to the haem group in haemoglobin, specifically to the Fe2+
• How many oxygen molecules can each haemoglobin molecule carry?

  Four
• The partial pressure of oxygen is a measure of oxygen concentration.
• As partial pressure increases, the affinity of haemoglobin for oxygen increases
• Steps in oxygen binding and release during respiration

  1️⃣ Oxygen binds to haemoglobin in the lungs

  2️⃣ Partial pressure decreases as oxygen is used in tissues

  3️⃣ Oxygen is released in respiring tissues

  4️⃣ Haemoglobin returns to the lungs
• What do dissociation curves illustrate?

  Haemoglobin saturation changes
• At high partial pressure, haemoglobin has high affinity for oxygen and is highly saturated.
• After binding to the first oxygen molecule, the affinity of haemoglobin for oxygen increases
• What is the term for the increased affinity of haemoglobin for oxygen after binding to the first molecule?

  Positive cooperativity
• Why does fetal haemoglobin have a higher affinity for oxygen than adult haemoglobin?

  Low oxygen saturation at placenta
• The Bohr effect describes the decrease in haemoglobin's affinity for oxygen in the presence of carbon dioxide.
• In the presence of carbon dioxide, the affinity of haemoglobin for oxygen decreases
• What is the effect of carbon dioxide on haemoglobin that leads to oxygen release?

  Acidic conditions
• Match the feature of a circulatory system with its function:

  Suitable medium ↔️ Allows substances to dissolve

  Heart ↔️ Maintains pressure differences

  Valves ↔️ Prevents backflow of blood

  Closed system of vessels ↔️ Delivers substances to all body parts
• The circulatory system in mammals is a closed double circulatory system
• Why does the heart have two pumps instead of one?

  Maintain blood pressure
• What is the pacemaker of the heart called?

  Sinoatrial node
• Steps in the cardiac cycle

  1️⃣ Cardiac diastole

  2️⃣ Atrial systole

  3️⃣ Ventricular systole
• What happens during atrial systole?

  Blood is forced into ventricles
• Veins have thin walls and valves to prevent the backflow of blood.
• What is the role of tissue fluid?

  Exchange oxygen and nutrients
• Water moves from tissue fluid to blood by osmosis
• What is the process by which water travels up the xylem in plants?

  Transpiration
• Phloem tissue transports sugars in plants through the active process of translocation.
• Xylem and phloem are components of the vascular bundle