<?xml version="1.0" encoding="us-ascii"?>
<!--XBRL document created with Toppan Merrill Bridge  9.6.8119.21675 -->
<!--Based on XBRL 2.1-->
<!--Created on: 5/16/2022 11:05:05 AM-->
<!--Modified on: 5/16/2022 11:05:05 AM-->
<xsd:schema xmlns:exch="http://xbrl.sec.gov/exch/2021" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:country="http://xbrl.sec.gov/country/2021" xmlns:naics="http://xbrl.sec.gov/naics/2021" xmlns:sic="http://xbrl.sec.gov/sic/2021" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:us-gaap="http://fasb.org/us-gaap/2021-01-31" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:stpr="http://xbrl.sec.gov/stpr/2021" xmlns:us-types="http://fasb.org/us-types/2021-01-31" xmlns:srt="http://fasb.org/srt/2021-01-31" xmlns:xl="http://www.xbrl.org/2003/XLink" xmlns:currency="http://xbrl.sec.gov/currency/2021" targetNamespace="http://www.protalix.com/20220331" elementFormDefault="qualified" xmlns:srt-types="http://fasb.org/srt-types/2021-01-31" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:dtr-types="http://www.xbrl.org/dtr/type/2020-01-21" xmlns:plx="http://www.protalix.com/20220331" xmlns:enum2="http://xbrl.org/2020/extensible-enumerations-2.0" xmlns:us-roles="http://fasb.org/us-roles/2021-01-31" xmlns:ref="http://www.xbrl.org/2006/ref" xmlns:srt-roles="http://fasb.org/srt-roles/2021-01-31" xmlns:utr="http://www.xbrl.org/2009/utr" xmlns:negated="http://www.xbrl.org/2009/role/negated" xmlns:attributeFormDefault="unqualified" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:deprecated="http://www.xbrl.org/2009/role/deprecated" xmlns:net="http://www.xbrl.org/2009/role/net" xmlns:dei="http://xbrl.sec.gov/dei/2021q4">
  <xsd:annotation>
    <xsd:appinfo>
      <link:roleType roleURI="http://www.protalix.com/role/DisclosureStandardAndCustomAxisDomainDefaults" id="DisclosureStandardAndCustomAxisDomainDefaults">
        <link:definition>99900 - Disclosure - Standard And Custom Axis Domain Defaults</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/StatementCondensedConsolidatedBalanceSheets" id="StatementCondensedConsolidatedBalanceSheets">
        <link:definition>00100 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/StatementCondensedConsolidatedStatementsOfOperations" id="StatementCondensedConsolidatedStatementsOfOperations">
        <link:definition>00200 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/StatementCondensedConsolidatedStatementsOfCashFlows" id="StatementCondensedConsolidatedStatementsOfCashFlows">
        <link:definition>00400 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/DisclosureInventoriesScheduleOfInventoryDetails" id="DisclosureInventoriesScheduleOfInventoryDetails">
        <link:definition>40201 - Disclosure - INVENTORIES (Schedule of Inventory) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/StatementCondensedConsolidatedStatementsOfOperationsParenthetical" id="StatementCondensedConsolidatedStatementsOfOperationsParenthetical">
        <link:definition>00205 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/StatementCondensedConsolidatedStatementsOfChangesInStockholdersEquityCapitalDeficiency" id="StatementCondensedConsolidatedStatementsOfChangesInStockholdersEquityCapitalDeficiency">
        <link:definition>00300 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (CAPITAL DEFICIENCY)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/StatementCondensedConsolidatedStatementsOfChangesInStockholdersEquityCapitalDeficiencyParenthetical" id="StatementCondensedConsolidatedStatementsOfChangesInStockholdersEquityCapitalDeficiencyParenthetical">
        <link:definition>00305 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (CAPITAL DEFICIENCY) (Parenthetical)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/DisclosureFairValueMeasurementTables" id="DisclosureFairValueMeasurementTables">
        <link:definition>30303 - Disclosure - FAIR VALUE MEASUREMENT (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/DisclosureSignificantAccountingPoliciesAdditionalInformationDetails" id="DisclosureSignificantAccountingPoliciesAdditionalInformationDetails">
        <link:definition>40101 - Disclosure - SIGNIFICANT ACCOUNTING POLICIES (Additional Information) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/DisclosureFairValueMeasurementScheduleOfFairValueAssumptionsDetails" id="DisclosureFairValueMeasurementScheduleOfFairValueAssumptionsDetails">
        <link:definition>40301 - Disclosure - FAIR VALUE MEASUREMENT (Schedule of Fair Value Assumptions) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/DisclosureFairValueMeasurementAdditionalInformationDetails" id="DisclosureFairValueMeasurementAdditionalInformationDetails">
        <link:definition>40302 - Disclosure - FAIR VALUE MEASUREMENT (Additional Information) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/DisclosureRevenuesDetails" id="DisclosureRevenuesDetails">
        <link:definition>40401 - Disclosure - REVENUES (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/DisclosureStockTransactionsDetails" id="DisclosureStockTransactionsDetails">
        <link:definition>40501 - Disclosure - STOCK TRANSACTIONS (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/DisclosureSubsequentEventsDetails" id="DisclosureSubsequentEventsDetails">
        <link:definition>40601 - Disclosure - SUBSEQUENT EVENTS (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/DocumentDocumentAndEntityInformation" id="DocumentDocumentAndEntityInformation">
        <link:definition>00090 - Document - Document and Entity Information</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/DisclosureSignificantAccountingPolicies" id="DisclosureSignificantAccountingPolicies">
        <link:definition>10101 - Disclosure - SIGNIFICANT ACCOUNTING POLICIES</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/DisclosureInventories" id="DisclosureInventories">
        <link:definition>10201 - Disclosure - INVENTORIES</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/DisclosureFairValueMeasurement" id="DisclosureFairValueMeasurement">
        <link:definition>10301 - Disclosure - FAIR VALUE MEASUREMENT</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/DisclosureRevenues" id="DisclosureRevenues">
        <link:definition>10401 - Disclosure - REVENUES</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/DisclosureStockTransactions" id="DisclosureStockTransactions">
        <link:definition>10501 - Disclosure - STOCK TRANSACTIONS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/DisclosureSubsequentEvents" id="DisclosureSubsequentEvents">
        <link:definition>10601 - Disclosure - SUBSEQUENT EVENTS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/DisclosureSignificantAccountingPoliciesPolicies" id="DisclosureSignificantAccountingPoliciesPolicies">
        <link:definition>20102 - Disclosure - SIGNIFICANT ACCOUNTING POLICIES (Policies)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/DisclosureInventoriesTables" id="DisclosureInventoriesTables">
        <link:definition>30203 - Disclosure - INVENTORIES (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.protalix.com/role/DisclosureRevenuesTables" id="DisclosureRevenuesTables">
        <link:definition>30403 - Disclosure - REVENUES (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:linkbaseRef xlink:type="simple" xlink:href="plx-20220331_pre.xml" xlink:role="http://www.xbrl.org/2003/role/presentationLinkbaseRef" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" />
      <link:linkbaseRef xlink:type="simple" xlink:href="plx-20220331_def.xml" xlink:role="http://www.xbrl.org/2003/role/definitionLinkbaseRef" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" />
      <link:linkbaseRef xlink:type="simple" xlink:href="plx-20220331_lab.xml" xlink:role="http://www.xbrl.org/2003/role/labelLinkbaseRef" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" />
      <link:linkbaseRef xlink:type="simple" xlink:href="plx-20220331_cal.xml" xlink:role="http://www.xbrl.org/2003/role/calculationLinkbaseRef" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" />
    </xsd:appinfo>
  </xsd:annotation>
  <xsd:import namespace="http://xbrl.sec.gov/dei/2021q4" schemaLocation="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd" />
  <xsd:import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd" />
  <xsd:import namespace="http://xbrl.org/2005/xbrldt" schemaLocation="http://www.xbrl.org/2005/xbrldt-2005.xsd" />
  <xsd:import namespace="http://www.xbrl.org/2009/role/negated" schemaLocation="http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd" />
  <xsd:import namespace="http://www.xbrl.org/dtr/type/2020-01-21" schemaLocation="https://www.xbrl.org/dtr/type/2020-01-21/types.xsd" />
  <xsd:import namespace="http://fasb.org/us-roles/2021-01-31" schemaLocation="https://xbrl.fasb.org/us-gaap/2021/elts/us-roles-2021-01-31.xsd" />
  <xsd:import namespace="http://fasb.org/us-gaap/2021-01-31" schemaLocation="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd" />
  <xsd:import namespace="http://fasb.org/srt/2021-01-31" schemaLocation="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd" />
  <xsd:import namespace="http://xbrl.sec.gov/country/2021" schemaLocation="https://xbrl.sec.gov/country/2021/country-2021.xsd" />
  <xsd:element name="ShareBasedCompensationRestrictedStockAwardsNetOfForfeitures" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="plx_ShareBasedCompensationRestrictedStockAwardsNetOfForfeitures" substitutionGroup="xbrli:item" xbrli:balance="credit" />
  <xsd:element id="plx_ShareBasedCompensationRestrictedStockAwardsNetOfForfeituresShares" name="ShareBasedCompensationRestrictedStockAwardsNetOfForfeituresShares" nillable="true" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" />
  <xsd:element id="plx_GainLossOnAmountsFundedInRespectOfEmployeeRightsUponRetirement" name="GainLossOnAmountsFundedInRespectOfEmployeeRightsUponRetirement" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" />
  <xsd:element name="ChangeInOperatingLeaseRightOfUseAssets" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="plx_ChangeInOperatingLeaseRightOfUseAssets" substitutionGroup="xbrli:item" xbrli:balance="credit" />
  <xsd:element id="plx_IncreaseInLiabilitiesForPropertyPlantAndEquipment" name="IncreaseInLiabilitiesForPropertyPlantAndEquipment" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" />
  <xsd:element id="plx_RevenueDisclosureTextBlock" name="RevenueDisclosureTextBlock" nillable="true" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" />
  <xsd:element name="NatureOfOperationsPolicyTextBlock" type="dtr-types:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="plx_NatureOfOperationsPolicyTextBlock" substitutionGroup="xbrli:item" />
  <xsd:element name="SignificantAccountingPoliciesTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="plx_SignificantAccountingPoliciesTable" substitutionGroup="xbrldt:hypercubeItem" />
  <xsd:element name="AmendedPfizerAgreementMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="plx_AmendedPfizerAgreementMember" substitutionGroup="xbrli:item" />
  <xsd:element name="ChiesiUSAgreementMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="plx_ChiesiUSAgreementMember" substitutionGroup="xbrli:item" />
  <xsd:element name="ChiesiExUSAgreementMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="plx_ChiesiExUSAgreementMember" substitutionGroup="xbrli:item" />
  <xsd:element name="ProtalixBioTherapeuticsIncorporationMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="plx_ProtalixBioTherapeuticsIncorporationMember" substitutionGroup="xbrli:item" />
  <xsd:element name="SignificantAccountingPoliciesLineItems" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="plx_SignificantAccountingPoliciesLineItems" substitutionGroup="xbrli:item" />
  <xsd:element id="plx_CollaborativeArrangementRevenuesExpensesSharingPercentage" name="CollaborativeArrangementRevenuesExpensesSharingPercentage" nillable="true" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" />
  <xsd:element id="plx_UpfrontNonrefundableNoncreditablePaymentReceivable" name="UpfrontNonrefundableNoncreditablePaymentReceivable" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="debit" />
  <xsd:element id="plx_AdditionalAmountsPayableToCoverDevelopmentCosts" name="AdditionalAmountsPayableToCoverDevelopmentCosts" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="debit" />
  <xsd:element name="MaximumEntitlementOfDevelopmentCostsToCoverPerYear" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" nillable="true" id="plx_MaximumEntitlementOfDevelopmentCostsToCoverPerYear" substitutionGroup="xbrli:item" xbrli:balance="debit" />
  <xsd:element name="PaymentOnNetSalesPercentage" type="dtr-types:percentItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="plx_PaymentOnNetSalesPercentage" substitutionGroup="xbrli:item" />
  <xsd:element name="SevenPointFivePercentageConvertibleNotesMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="plx_SevenPointFivePercentageConvertibleNotesMember" substitutionGroup="xbrli:item" />
  <xsd:element id="plx_PfizerMember" name="PfizerMember" nillable="true" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <xsd:element id="plx_EmployeeStockIncentivePlan2006Member" name="EmployeeStockIncentivePlan2006Member" nillable="true" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <xsd:element id="plx_MaintainOfMinimumCashBalance" name="MaintainOfMinimumCashBalance" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="debit" />
  <xsd:element id="plx_ChiesiMember" name="ChiesiMember" nillable="true" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <xsd:element id="plx_ChiesiUsAgreementAndChiesiExUsAgreementMember" name="ChiesiUsAgreementAndChiesiExUsAgreementMember" nillable="true" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <xsd:element id="plx_ShortTermBankDeposits" name="ShortTermBankDeposits" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="debit" />
  <xsd:element id="plx_IncreaseDecreaseInBankDeposits" name="IncreaseDecreaseInBankDeposits" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" />
  <xsd:element id="plx_AlfataligliceraseMember" name="AlfataligliceraseMember" nillable="true" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <xsd:element id="plx_ChiesiAgreementsMember" name="ChiesiAgreementsMember" nillable="true" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <xsd:element id="plx_MeasurementInputYieldMember" name="MeasurementInputYieldMember" nillable="true" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <xsd:element id="plx_IncreaseDecreaseInRestrictedDeposit" name="IncreaseDecreaseInRestrictedDeposit" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" />
  <xsd:element id="plx_SaleOfStockMaximumOfferingPrice" name="SaleOfStockMaximumOfferingPrice" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" />
  <xsd:element id="plx_AtMarketEquityOfferingMember" name="AtMarketEquityOfferingMember" nillable="true" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <xsd:element id="plx_InterestReceivedNet" name="InterestReceivedNet" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="debit" />
  <xsd:element id="plx_AdditionalAmountPayableForAchievementOfRegulatoryAndCommercialMilestones" name="AdditionalAmountPayableForAchievementOfRegulatoryAndCommercialMilestones" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="debit" />
  <xsd:element id="plx_ProceedsFromIssuanceOfCommonStockAndWarrantsNetOfIssuanceCost" name="ProceedsFromIssuanceOfCommonStockAndWarrantsNetOfIssuanceCost" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="debit" />
  <xsd:element id="plx_StockIssuedDuringPeriodSharesSalesAgreement" name="StockIssuedDuringPeriodSharesSalesAgreement" nillable="true" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" />
  <xsd:element id="plx_StockIssuedDuringPeriodValueSalesAgreement" name="StockIssuedDuringPeriodValueSalesAgreement" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" />
  <xsd:element id="plx_ProceedsFromSaleOfShortTermDeposits" name="ProceedsFromSaleOfShortTermDeposits" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="debit" />
  <xsd:element id="plx_AgreementAmendmentPaymentReceivable" name="AgreementAmendmentPaymentReceivable" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="debit" />
  <xsd:element id="plx_ChangeInAmountReceivableForAchievementOfRegulatoryAndCommercialMilestones" name="ChangeInAmountReceivableForAchievementOfRegulatoryAndCommercialMilestones" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="debit" />
  <xsd:element id="plx_RevenuePerformanceObligationNumber" name="RevenuePerformanceObligationNumber" nillable="true" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" />
  <xsd:element id="plx_SevenPointFivePercentageSeniorSecuredConvertibleNotesDue2024Member" name="SevenPointFivePercentageSeniorSecuredConvertibleNotesDue2024Member" nillable="true" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="SupplyAndTechnologyTransferAgreementWithFiocruzMember" id="plx_SupplyAndTechnologyTransferAgreementWithFiocruzMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="ProceedsFromExpenseReimbursements" id="plx_ProceedsFromExpenseReimbursements" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" xbrli:balance="debit" />
  <xsd:element name="ConvertibleNotesDue2021And2024Member" id="plx_ConvertibleNotesDue2021And2024Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="ProceedsFromSaleOfProducts" id="plx_ProceedsFromSaleOfProducts" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" xbrli:balance="debit" />
</xsd:schema>
