Which of the following is an incorrect statement? a. gastrovascular cavities have a single opening through which animals both ingest food and expel wastes. b. extracellular digestion is the process in which food is broken down outside cells in a digestive system. c. intracellular digestion happens when animals digest food inside specialized cells that pass nutrients to other cells by diffusion. d. digestive tracts have 2 openings, which allows food to move in 2 directions.

The incorrect statement is option D. Digestive tracts have two openings, which allows food to move in two directions.

Explanation:

The digestive system is a long twisted tube from the mouth to the anus with a series of accessory organs connected to it. This long twisted continuous tube having two openings, mouth and the anus, called the digestive tract that allows food to move in one direction only (mouth to anus).

In the digestive tract, food enters from the mouth and food passing through pharynx, esophagus, stomach, small intestine, and large intestine. The indigestible food or waste eliminated through the anus.

So, the digestive tract allows food to move in one direction only.

Thus, incorrect option would be option D.

a. CO2 is produced ---> occurs predominantly at the peripheral tissues

b. CO2 + H20 to form H2CO3 ---> occurs predominantly at the peripheral tissues

c. Bicarbonate combines with H+ to form H2CO3 ---> occurs predominantly in the lungs

d. CO2 diffuses into blood ---> occurs predominantly at the peripheral tissues

Explanation:

Peripheral gas exchange or internal respiration is the gaseous exchange that occurs between the blood and the tissues of the body across the walls of the peripheral capillaries in contrast to external respiration which is the exchange of respiratory gase, carbon (iv) oxide and oxygen, between the body and the external environment occuring at the lungs.

During respiration, carbon dioxide is removed from the body through the lungs while oxygen is taken into through the lungs.

Carbon dioxide is produced as a waste product of metabolism by the tissues of the body. Removal of carbon dioxide is of utmost importance and occurs in three distinct ways in the body:

1. First carbon dioxide is transported in dissolved form in the blood to the lungs.

2. Carbon dioxide combines reversibly with hemoglobin to form carbaminohemoglobin and is transported to the lungs where it dissociates from hemoglobin is removed via expiration

3. Carbon dioxide is transported in the form of bicarbonate in blood to the lungs where it removed by the following process : i) carbon dioxide produced in the peripheral tissues diffusers into the and into the red blood cells. (ii) The enzyme carbonic anhydrase converts it to carbonic acid (iii) Carbonic acid dissociates into bicarbonate and hydrogen ions. Hydrogen ions binds to haemoglobin while bicarbonate is exchange with chloride ion in the plasma. (iv) Bicarbonate is transported to the lungs in blood plasma. (v) At the lungs, bicarbonate renters the red blood cells in exchange for chloride ions. The bicarbonate combines with hydrogen ions released from hemoglobin to form carbonic acid. Carbonic acid is broken down to carbon dioxide and water by carbonic anhydrase in the red blood cells. Carbon dioxide diffusesout into the lungs and is expelled.

Therefore, the processes in the question above can be classified thus:

a. CO2 is produced ---> occurs predominantly at the peripheral tissues

b. CO2 H20 to form H2CO3 ---> occurs predominantly at the peripheral tissues

c. Bicarbonate combines with H+ to form H2CO3 ---> occurs predominantly in the lungs

d. CO2 diffuses into blood ---> occurs predominantly at the peripheral tissues